5201 lines
164 KiB
C
5201 lines
164 KiB
C
/*-------------------------------------------------------------------------
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*
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* predicate.c
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* POSTGRES predicate locking
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* to support full serializable transaction isolation
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*
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*
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* The approach taken is to implement Serializable Snapshot Isolation (SSI)
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* as initially described in this paper:
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*
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* Michael J. Cahill, Uwe Röhm, and Alan D. Fekete. 2008.
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* Serializable isolation for snapshot databases.
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* In SIGMOD '08: Proceedings of the 2008 ACM SIGMOD
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* international conference on Management of data,
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* pages 729-738, New York, NY, USA. ACM.
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* http://doi.acm.org/10.1145/1376616.1376690
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*
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* and further elaborated in Cahill's doctoral thesis:
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*
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* Michael James Cahill. 2009.
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* Serializable Isolation for Snapshot Databases.
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* Sydney Digital Theses.
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* University of Sydney, School of Information Technologies.
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* http://hdl.handle.net/2123/5353
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*
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*
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* Predicate locks for Serializable Snapshot Isolation (SSI) are SIREAD
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* locks, which are so different from normal locks that a distinct set of
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* structures is required to handle them. They are needed to detect
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* rw-conflicts when the read happens before the write. (When the write
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* occurs first, the reading transaction can check for a conflict by
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* examining the MVCC data.)
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*
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* (1) Besides tuples actually read, they must cover ranges of tuples
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* which would have been read based on the predicate. This will
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* require modelling the predicates through locks against database
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* objects such as pages, index ranges, or entire tables.
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*
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* (2) They must be kept in RAM for quick access. Because of this, it
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* isn't possible to always maintain tuple-level granularity -- when
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* the space allocated to store these approaches exhaustion, a
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* request for a lock may need to scan for situations where a single
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* transaction holds many fine-grained locks which can be coalesced
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* into a single coarser-grained lock.
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*
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* (3) They never block anything; they are more like flags than locks
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* in that regard; although they refer to database objects and are
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* used to identify rw-conflicts with normal write locks.
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*
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* (4) While they are associated with a transaction, they must survive
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* a successful COMMIT of that transaction, and remain until all
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* overlapping transactions complete. This even means that they
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* must survive termination of the transaction's process. If a
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* top level transaction is rolled back, however, it is immediately
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* flagged so that it can be ignored, and its SIREAD locks can be
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* released any time after that.
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*
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* (5) The only transactions which create SIREAD locks or check for
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* conflicts with them are serializable transactions.
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*
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* (6) When a write lock for a top level transaction is found to cover
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* an existing SIREAD lock for the same transaction, the SIREAD lock
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* can be deleted.
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*
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* (7) A write from a serializable transaction must ensure that an xact
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* record exists for the transaction, with the same lifespan (until
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* all concurrent transaction complete or the transaction is rolled
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* back) so that rw-dependencies to that transaction can be
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* detected.
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*
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* We use an optimization for read-only transactions. Under certain
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* circumstances, a read-only transaction's snapshot can be shown to
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* never have conflicts with other transactions. This is referred to
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* as a "safe" snapshot (and one known not to be is "unsafe").
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* However, it can't be determined whether a snapshot is safe until
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* all concurrent read/write transactions complete.
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*
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* Once a read-only transaction is known to have a safe snapshot, it
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* can release its predicate locks and exempt itself from further
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* predicate lock tracking. READ ONLY DEFERRABLE transactions run only
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* on safe snapshots, waiting as necessary for one to be available.
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*
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*
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* Lightweight locks to manage access to the predicate locking shared
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* memory objects must be taken in this order, and should be released in
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* reverse order:
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*
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* SerializableFinishedListLock
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* - Protects the list of transactions which have completed but which
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* may yet matter because they overlap still-active transactions.
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*
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* SerializablePredicateLockListLock
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* - Protects the linked list of locks held by a transaction. Note
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* that the locks themselves are also covered by the partition
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* locks of their respective lock targets; this lock only affects
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* the linked list connecting the locks related to a transaction.
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* - All transactions share this single lock (with no partitioning).
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* - There is never a need for a process other than the one running
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* an active transaction to walk the list of locks held by that
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* transaction, except parallel query workers sharing the leader's
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* transaction. In the parallel case, an extra per-sxact lock is
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* taken; see below.
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* - It is relatively infrequent that another process needs to
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* modify the list for a transaction, but it does happen for such
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* things as index page splits for pages with predicate locks and
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* freeing of predicate locked pages by a vacuum process. When
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* removing a lock in such cases, the lock itself contains the
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* pointers needed to remove it from the list. When adding a
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* lock in such cases, the lock can be added using the anchor in
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* the transaction structure. Neither requires walking the list.
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* - Cleaning up the list for a terminated transaction is sometimes
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* not done on a retail basis, in which case no lock is required.
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* - Due to the above, a process accessing its active transaction's
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* list always uses a shared lock, regardless of whether it is
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* walking or maintaining the list. This improves concurrency
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* for the common access patterns.
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* - A process which needs to alter the list of a transaction other
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* than its own active transaction must acquire an exclusive
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* lock.
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*
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* SERIALIZABLEXACT's member 'predicateLockListLock'
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* - Protects the linked list of locks held by a transaction. Only
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* needed for parallel mode, where multiple backends share the
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* same SERIALIZABLEXACT object. Not needed if
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* SerializablePredicateLockListLock is held exclusively.
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*
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* PredicateLockHashPartitionLock(hashcode)
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* - The same lock protects a target, all locks on that target, and
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* the linked list of locks on the target.
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* - When more than one is needed, acquire in ascending address order.
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* - When all are needed (rare), acquire in ascending index order with
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* PredicateLockHashPartitionLockByIndex(index).
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*
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* SerializableXactHashLock
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* - Protects both PredXact and SerializableXidHash.
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*
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*
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* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/backend/storage/lmgr/predicate.c
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*
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*-------------------------------------------------------------------------
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*/
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/*
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* INTERFACE ROUTINES
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*
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* housekeeping for setting up shared memory predicate lock structures
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* InitPredicateLocks(void)
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* PredicateLockShmemSize(void)
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*
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* predicate lock reporting
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* GetPredicateLockStatusData(void)
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* PageIsPredicateLocked(Relation relation, BlockNumber blkno)
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*
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* predicate lock maintenance
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* GetSerializableTransactionSnapshot(Snapshot snapshot)
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* SetSerializableTransactionSnapshot(Snapshot snapshot,
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* VirtualTransactionId *sourcevxid)
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* RegisterPredicateLockingXid(void)
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* PredicateLockRelation(Relation relation, Snapshot snapshot)
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* PredicateLockPage(Relation relation, BlockNumber blkno,
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* Snapshot snapshot)
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* PredicateLockTuple(Relation relation, HeapTuple tuple,
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* Snapshot snapshot)
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* PredicateLockPageSplit(Relation relation, BlockNumber oldblkno,
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* BlockNumber newblkno)
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* PredicateLockPageCombine(Relation relation, BlockNumber oldblkno,
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* BlockNumber newblkno)
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* TransferPredicateLocksToHeapRelation(Relation relation)
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* ReleasePredicateLocks(bool isCommit, bool isReadOnlySafe)
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*
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* conflict detection (may also trigger rollback)
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* CheckForSerializableConflictOut(bool visible, Relation relation,
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* HeapTupleData *tup, Buffer buffer,
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* Snapshot snapshot)
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* CheckForSerializableConflictIn(Relation relation, HeapTupleData *tup,
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* Buffer buffer)
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* CheckTableForSerializableConflictIn(Relation relation)
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*
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* final rollback checking
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* PreCommit_CheckForSerializationFailure(void)
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*
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* two-phase commit support
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* AtPrepare_PredicateLocks(void);
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* PostPrepare_PredicateLocks(TransactionId xid);
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* PredicateLockTwoPhaseFinish(TransactionId xid, bool isCommit);
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* predicatelock_twophase_recover(TransactionId xid, uint16 info,
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* void *recdata, uint32 len);
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*/
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#include "postgres.h"
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#include "access/heapam.h"
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#include "access/htup_details.h"
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#include "access/parallel.h"
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#include "access/slru.h"
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#include "access/subtrans.h"
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#include "access/transam.h"
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#include "access/twophase.h"
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#include "access/twophase_rmgr.h"
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#include "access/xact.h"
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#include "access/xlog.h"
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#include "miscadmin.h"
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#include "pgstat.h"
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#include "storage/bufmgr.h"
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#include "storage/predicate.h"
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#include "storage/predicate_internals.h"
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#include "storage/proc.h"
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#include "storage/procarray.h"
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#include "utils/rel.h"
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#include "utils/snapmgr.h"
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/* Uncomment the next line to test the graceful degradation code. */
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/* #define TEST_OLDSERXID */
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/*
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* Test the most selective fields first, for performance.
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*
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* a is covered by b if all of the following hold:
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* 1) a.database = b.database
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* 2) a.relation = b.relation
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* 3) b.offset is invalid (b is page-granularity or higher)
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* 4) either of the following:
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* 4a) a.offset is valid (a is tuple-granularity) and a.page = b.page
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* or 4b) a.offset is invalid and b.page is invalid (a is
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* page-granularity and b is relation-granularity
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*/
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#define TargetTagIsCoveredBy(covered_target, covering_target) \
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((GET_PREDICATELOCKTARGETTAG_RELATION(covered_target) == /* (2) */ \
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GET_PREDICATELOCKTARGETTAG_RELATION(covering_target)) \
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&& (GET_PREDICATELOCKTARGETTAG_OFFSET(covering_target) == \
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InvalidOffsetNumber) /* (3) */ \
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&& (((GET_PREDICATELOCKTARGETTAG_OFFSET(covered_target) != \
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InvalidOffsetNumber) /* (4a) */ \
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&& (GET_PREDICATELOCKTARGETTAG_PAGE(covering_target) == \
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GET_PREDICATELOCKTARGETTAG_PAGE(covered_target))) \
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|| ((GET_PREDICATELOCKTARGETTAG_PAGE(covering_target) == \
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InvalidBlockNumber) /* (4b) */ \
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&& (GET_PREDICATELOCKTARGETTAG_PAGE(covered_target) \
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!= InvalidBlockNumber))) \
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&& (GET_PREDICATELOCKTARGETTAG_DB(covered_target) == /* (1) */ \
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GET_PREDICATELOCKTARGETTAG_DB(covering_target)))
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/*
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* The predicate locking target and lock shared hash tables are partitioned to
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* reduce contention. To determine which partition a given target belongs to,
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* compute the tag's hash code with PredicateLockTargetTagHashCode(), then
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* apply one of these macros.
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* NB: NUM_PREDICATELOCK_PARTITIONS must be a power of 2!
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*/
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#define PredicateLockHashPartition(hashcode) \
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((hashcode) % NUM_PREDICATELOCK_PARTITIONS)
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#define PredicateLockHashPartitionLock(hashcode) \
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(&MainLWLockArray[PREDICATELOCK_MANAGER_LWLOCK_OFFSET + \
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PredicateLockHashPartition(hashcode)].lock)
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#define PredicateLockHashPartitionLockByIndex(i) \
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(&MainLWLockArray[PREDICATELOCK_MANAGER_LWLOCK_OFFSET + (i)].lock)
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#define NPREDICATELOCKTARGETENTS() \
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mul_size(max_predicate_locks_per_xact, add_size(MaxBackends, max_prepared_xacts))
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#define SxactIsOnFinishedList(sxact) (!SHMQueueIsDetached(&((sxact)->finishedLink)))
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/*
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* Note that a sxact is marked "prepared" once it has passed
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* PreCommit_CheckForSerializationFailure, even if it isn't using
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* 2PC. This is the point at which it can no longer be aborted.
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*
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* The PREPARED flag remains set after commit, so SxactIsCommitted
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* implies SxactIsPrepared.
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*/
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#define SxactIsCommitted(sxact) (((sxact)->flags & SXACT_FLAG_COMMITTED) != 0)
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#define SxactIsPrepared(sxact) (((sxact)->flags & SXACT_FLAG_PREPARED) != 0)
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#define SxactIsRolledBack(sxact) (((sxact)->flags & SXACT_FLAG_ROLLED_BACK) != 0)
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#define SxactIsDoomed(sxact) (((sxact)->flags & SXACT_FLAG_DOOMED) != 0)
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#define SxactIsReadOnly(sxact) (((sxact)->flags & SXACT_FLAG_READ_ONLY) != 0)
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#define SxactHasSummaryConflictIn(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_IN) != 0)
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#define SxactHasSummaryConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_SUMMARY_CONFLICT_OUT) != 0)
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/*
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* The following macro actually means that the specified transaction has a
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* conflict out *to a transaction which committed ahead of it*. It's hard
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* to get that into a name of a reasonable length.
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*/
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#define SxactHasConflictOut(sxact) (((sxact)->flags & SXACT_FLAG_CONFLICT_OUT) != 0)
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#define SxactIsDeferrableWaiting(sxact) (((sxact)->flags & SXACT_FLAG_DEFERRABLE_WAITING) != 0)
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#define SxactIsROSafe(sxact) (((sxact)->flags & SXACT_FLAG_RO_SAFE) != 0)
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#define SxactIsROUnsafe(sxact) (((sxact)->flags & SXACT_FLAG_RO_UNSAFE) != 0)
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#define SxactIsPartiallyReleased(sxact) (((sxact)->flags & SXACT_FLAG_PARTIALLY_RELEASED) != 0)
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/*
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* Compute the hash code associated with a PREDICATELOCKTARGETTAG.
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*
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* To avoid unnecessary recomputations of the hash code, we try to do this
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* just once per function, and then pass it around as needed. Aside from
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* passing the hashcode to hash_search_with_hash_value(), we can extract
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* the lock partition number from the hashcode.
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*/
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#define PredicateLockTargetTagHashCode(predicatelocktargettag) \
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get_hash_value(PredicateLockTargetHash, predicatelocktargettag)
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/*
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* Given a predicate lock tag, and the hash for its target,
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* compute the lock hash.
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*
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* To make the hash code also depend on the transaction, we xor the sxid
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* struct's address into the hash code, left-shifted so that the
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* partition-number bits don't change. Since this is only a hash, we
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* don't care if we lose high-order bits of the address; use an
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* intermediate variable to suppress cast-pointer-to-int warnings.
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*/
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#define PredicateLockHashCodeFromTargetHashCode(predicatelocktag, targethash) \
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((targethash) ^ ((uint32) PointerGetDatum((predicatelocktag)->myXact)) \
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<< LOG2_NUM_PREDICATELOCK_PARTITIONS)
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/*
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* The SLRU buffer area through which we access the old xids.
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*/
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static SlruCtlData OldSerXidSlruCtlData;
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#define OldSerXidSlruCtl (&OldSerXidSlruCtlData)
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#define OLDSERXID_PAGESIZE BLCKSZ
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#define OLDSERXID_ENTRYSIZE sizeof(SerCommitSeqNo)
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#define OLDSERXID_ENTRIESPERPAGE (OLDSERXID_PAGESIZE / OLDSERXID_ENTRYSIZE)
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/*
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* Set maximum pages based on the number needed to track all transactions.
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*/
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#define OLDSERXID_MAX_PAGE (MaxTransactionId / OLDSERXID_ENTRIESPERPAGE)
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#define OldSerXidNextPage(page) (((page) >= OLDSERXID_MAX_PAGE) ? 0 : (page) + 1)
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#define OldSerXidValue(slotno, xid) (*((SerCommitSeqNo *) \
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(OldSerXidSlruCtl->shared->page_buffer[slotno] + \
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((((uint32) (xid)) % OLDSERXID_ENTRIESPERPAGE) * OLDSERXID_ENTRYSIZE))))
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#define OldSerXidPage(xid) (((uint32) (xid)) / OLDSERXID_ENTRIESPERPAGE)
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typedef struct OldSerXidControlData
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{
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int headPage; /* newest initialized page */
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TransactionId headXid; /* newest valid Xid in the SLRU */
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TransactionId tailXid; /* oldest xmin we might be interested in */
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} OldSerXidControlData;
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typedef struct OldSerXidControlData *OldSerXidControl;
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static OldSerXidControl oldSerXidControl;
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/*
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* When the oldest committed transaction on the "finished" list is moved to
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* SLRU, its predicate locks will be moved to this "dummy" transaction,
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* collapsing duplicate targets. When a duplicate is found, the later
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* commitSeqNo is used.
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*/
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static SERIALIZABLEXACT *OldCommittedSxact;
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/*
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* These configuration variables are used to set the predicate lock table size
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* and to control promotion of predicate locks to coarser granularity in an
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* attempt to degrade performance (mostly as false positive serialization
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* failure) gracefully in the face of memory pressure.
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*/
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int max_predicate_locks_per_xact; /* set by guc.c */
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int max_predicate_locks_per_relation; /* set by guc.c */
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int max_predicate_locks_per_page; /* set by guc.c */
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/*
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* This provides a list of objects in order to track transactions
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* participating in predicate locking. Entries in the list are fixed size,
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* and reside in shared memory. The memory address of an entry must remain
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* fixed during its lifetime. The list will be protected from concurrent
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* update externally; no provision is made in this code to manage that. The
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* number of entries in the list, and the size allowed for each entry is
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* fixed upon creation.
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*/
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static PredXactList PredXact;
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/*
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* This provides a pool of RWConflict data elements to use in conflict lists
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* between transactions.
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*/
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static RWConflictPoolHeader RWConflictPool;
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/*
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* The predicate locking hash tables are in shared memory.
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* Each backend keeps pointers to them.
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*/
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static HTAB *SerializableXidHash;
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static HTAB *PredicateLockTargetHash;
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static HTAB *PredicateLockHash;
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static SHM_QUEUE *FinishedSerializableTransactions;
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/*
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* Tag for a dummy entry in PredicateLockTargetHash. By temporarily removing
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* this entry, you can ensure that there's enough scratch space available for
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* inserting one entry in the hash table. This is an otherwise-invalid tag.
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*/
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static const PREDICATELOCKTARGETTAG ScratchTargetTag = {0, 0, 0, 0};
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static uint32 ScratchTargetTagHash;
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static LWLock *ScratchPartitionLock;
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/*
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* The local hash table used to determine when to combine multiple fine-
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* grained locks into a single courser-grained lock.
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*/
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static HTAB *LocalPredicateLockHash = NULL;
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/*
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* Keep a pointer to the currently-running serializable transaction (if any)
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* for quick reference. Also, remember if we have written anything that could
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* cause a rw-conflict.
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*/
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static SERIALIZABLEXACT *MySerializableXact = InvalidSerializableXact;
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static bool MyXactDidWrite = false;
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/*
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* The SXACT_FLAG_RO_UNSAFE optimization might lead us to release
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* MySerializableXact early. If that happens in a parallel query, the leader
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* needs to defer the destruction of the SERIALIZABLEXACT until end of
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* transaction, because the workers still have a reference to it. In that
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* case, the leader stores it here.
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*/
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static SERIALIZABLEXACT *SavedSerializableXact = InvalidSerializableXact;
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/* local functions */
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static SERIALIZABLEXACT *CreatePredXact(void);
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static void ReleasePredXact(SERIALIZABLEXACT *sxact);
|
|
static SERIALIZABLEXACT *FirstPredXact(void);
|
|
static SERIALIZABLEXACT *NextPredXact(SERIALIZABLEXACT *sxact);
|
|
|
|
static bool RWConflictExists(const SERIALIZABLEXACT *reader, const SERIALIZABLEXACT *writer);
|
|
static void SetRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer);
|
|
static void SetPossibleUnsafeConflict(SERIALIZABLEXACT *roXact, SERIALIZABLEXACT *activeXact);
|
|
static void ReleaseRWConflict(RWConflict conflict);
|
|
static void FlagSxactUnsafe(SERIALIZABLEXACT *sxact);
|
|
|
|
static bool OldSerXidPagePrecedesLogically(int p, int q);
|
|
static void OldSerXidInit(void);
|
|
static void OldSerXidAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo);
|
|
static SerCommitSeqNo OldSerXidGetMinConflictCommitSeqNo(TransactionId xid);
|
|
static void OldSerXidSetActiveSerXmin(TransactionId xid);
|
|
|
|
static uint32 predicatelock_hash(const void *key, Size keysize);
|
|
static void SummarizeOldestCommittedSxact(void);
|
|
static Snapshot GetSafeSnapshot(Snapshot snapshot);
|
|
static Snapshot GetSerializableTransactionSnapshotInt(Snapshot snapshot,
|
|
VirtualTransactionId *sourcevxid,
|
|
int sourcepid);
|
|
static bool PredicateLockExists(const PREDICATELOCKTARGETTAG *targettag);
|
|
static bool GetParentPredicateLockTag(const PREDICATELOCKTARGETTAG *tag,
|
|
PREDICATELOCKTARGETTAG *parent);
|
|
static bool CoarserLockCovers(const PREDICATELOCKTARGETTAG *newtargettag);
|
|
static void RemoveScratchTarget(bool lockheld);
|
|
static void RestoreScratchTarget(bool lockheld);
|
|
static void RemoveTargetIfNoLongerUsed(PREDICATELOCKTARGET *target,
|
|
uint32 targettaghash);
|
|
static void DeleteChildTargetLocks(const PREDICATELOCKTARGETTAG *newtargettag);
|
|
static int MaxPredicateChildLocks(const PREDICATELOCKTARGETTAG *tag);
|
|
static bool CheckAndPromotePredicateLockRequest(const PREDICATELOCKTARGETTAG *reqtag);
|
|
static void DecrementParentLocks(const PREDICATELOCKTARGETTAG *targettag);
|
|
static void CreatePredicateLock(const PREDICATELOCKTARGETTAG *targettag,
|
|
uint32 targettaghash,
|
|
SERIALIZABLEXACT *sxact);
|
|
static void DeleteLockTarget(PREDICATELOCKTARGET *target, uint32 targettaghash);
|
|
static bool TransferPredicateLocksToNewTarget(PREDICATELOCKTARGETTAG oldtargettag,
|
|
PREDICATELOCKTARGETTAG newtargettag,
|
|
bool removeOld);
|
|
static void PredicateLockAcquire(const PREDICATELOCKTARGETTAG *targettag);
|
|
static void DropAllPredicateLocksFromTable(Relation relation,
|
|
bool transfer);
|
|
static void SetNewSxactGlobalXmin(void);
|
|
static void ClearOldPredicateLocks(void);
|
|
static void ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
|
|
bool summarize);
|
|
static bool XidIsConcurrent(TransactionId xid);
|
|
static void CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag);
|
|
static void FlagRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer);
|
|
static void OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
|
|
SERIALIZABLEXACT *writer);
|
|
static void CreateLocalPredicateLockHash(void);
|
|
static void ReleasePredicateLocksLocal(void);
|
|
|
|
|
|
/*------------------------------------------------------------------------*/
|
|
|
|
/*
|
|
* Does this relation participate in predicate locking? Temporary and system
|
|
* relations are exempt, as are materialized views.
|
|
*/
|
|
static inline bool
|
|
PredicateLockingNeededForRelation(Relation relation)
|
|
{
|
|
return !(relation->rd_id < FirstBootstrapObjectId ||
|
|
RelationUsesLocalBuffers(relation) ||
|
|
relation->rd_rel->relkind == RELKIND_MATVIEW);
|
|
}
|
|
|
|
/*
|
|
* When a public interface method is called for a read, this is the test to
|
|
* see if we should do a quick return.
|
|
*
|
|
* Note: this function has side-effects! If this transaction has been flagged
|
|
* as RO-safe since the last call, we release all predicate locks and reset
|
|
* MySerializableXact. That makes subsequent calls to return quickly.
|
|
*
|
|
* This is marked as 'inline' to eliminate the function call overhead in the
|
|
* common case that serialization is not needed.
|
|
*/
|
|
static inline bool
|
|
SerializationNeededForRead(Relation relation, Snapshot snapshot)
|
|
{
|
|
/* Nothing to do if this is not a serializable transaction */
|
|
if (MySerializableXact == InvalidSerializableXact)
|
|
return false;
|
|
|
|
/*
|
|
* Don't acquire locks or conflict when scanning with a special snapshot.
|
|
* This excludes things like CLUSTER and REINDEX. They use the wholesale
|
|
* functions TransferPredicateLocksToHeapRelation() and
|
|
* CheckTableForSerializableConflictIn() to participate in serialization,
|
|
* but the scans involved don't need serialization.
|
|
*/
|
|
if (!IsMVCCSnapshot(snapshot))
|
|
return false;
|
|
|
|
/*
|
|
* Check if we have just become "RO-safe". If we have, immediately release
|
|
* all locks as they're not needed anymore. This also resets
|
|
* MySerializableXact, so that subsequent calls to this function can exit
|
|
* quickly.
|
|
*
|
|
* A transaction is flagged as RO_SAFE if all concurrent R/W transactions
|
|
* commit without having conflicts out to an earlier snapshot, thus
|
|
* ensuring that no conflicts are possible for this transaction.
|
|
*/
|
|
if (SxactIsROSafe(MySerializableXact))
|
|
{
|
|
ReleasePredicateLocks(false, true);
|
|
return false;
|
|
}
|
|
|
|
/* Check if the relation doesn't participate in predicate locking */
|
|
if (!PredicateLockingNeededForRelation(relation))
|
|
return false;
|
|
|
|
return true; /* no excuse to skip predicate locking */
|
|
}
|
|
|
|
/*
|
|
* Like SerializationNeededForRead(), but called on writes.
|
|
* The logic is the same, but there is no snapshot and we can't be RO-safe.
|
|
*/
|
|
static inline bool
|
|
SerializationNeededForWrite(Relation relation)
|
|
{
|
|
/* Nothing to do if this is not a serializable transaction */
|
|
if (MySerializableXact == InvalidSerializableXact)
|
|
return false;
|
|
|
|
/* Check if the relation doesn't participate in predicate locking */
|
|
if (!PredicateLockingNeededForRelation(relation))
|
|
return false;
|
|
|
|
return true; /* no excuse to skip predicate locking */
|
|
}
|
|
|
|
|
|
/*------------------------------------------------------------------------*/
|
|
|
|
/*
|
|
* These functions are a simple implementation of a list for this specific
|
|
* type of struct. If there is ever a generalized shared memory list, we
|
|
* should probably switch to that.
|
|
*/
|
|
static SERIALIZABLEXACT *
|
|
CreatePredXact(void)
|
|
{
|
|
PredXactListElement ptle;
|
|
|
|
ptle = (PredXactListElement)
|
|
SHMQueueNext(&PredXact->availableList,
|
|
&PredXact->availableList,
|
|
offsetof(PredXactListElementData, link));
|
|
if (!ptle)
|
|
return NULL;
|
|
|
|
SHMQueueDelete(&ptle->link);
|
|
SHMQueueInsertBefore(&PredXact->activeList, &ptle->link);
|
|
return &ptle->sxact;
|
|
}
|
|
|
|
static void
|
|
ReleasePredXact(SERIALIZABLEXACT *sxact)
|
|
{
|
|
PredXactListElement ptle;
|
|
|
|
Assert(ShmemAddrIsValid(sxact));
|
|
|
|
ptle = (PredXactListElement)
|
|
(((char *) sxact)
|
|
- offsetof(PredXactListElementData, sxact)
|
|
+ offsetof(PredXactListElementData, link));
|
|
SHMQueueDelete(&ptle->link);
|
|
SHMQueueInsertBefore(&PredXact->availableList, &ptle->link);
|
|
}
|
|
|
|
static SERIALIZABLEXACT *
|
|
FirstPredXact(void)
|
|
{
|
|
PredXactListElement ptle;
|
|
|
|
ptle = (PredXactListElement)
|
|
SHMQueueNext(&PredXact->activeList,
|
|
&PredXact->activeList,
|
|
offsetof(PredXactListElementData, link));
|
|
if (!ptle)
|
|
return NULL;
|
|
|
|
return &ptle->sxact;
|
|
}
|
|
|
|
static SERIALIZABLEXACT *
|
|
NextPredXact(SERIALIZABLEXACT *sxact)
|
|
{
|
|
PredXactListElement ptle;
|
|
|
|
Assert(ShmemAddrIsValid(sxact));
|
|
|
|
ptle = (PredXactListElement)
|
|
(((char *) sxact)
|
|
- offsetof(PredXactListElementData, sxact)
|
|
+ offsetof(PredXactListElementData, link));
|
|
ptle = (PredXactListElement)
|
|
SHMQueueNext(&PredXact->activeList,
|
|
&ptle->link,
|
|
offsetof(PredXactListElementData, link));
|
|
if (!ptle)
|
|
return NULL;
|
|
|
|
return &ptle->sxact;
|
|
}
|
|
|
|
/*------------------------------------------------------------------------*/
|
|
|
|
/*
|
|
* These functions manage primitive access to the RWConflict pool and lists.
|
|
*/
|
|
static bool
|
|
RWConflictExists(const SERIALIZABLEXACT *reader, const SERIALIZABLEXACT *writer)
|
|
{
|
|
RWConflict conflict;
|
|
|
|
Assert(reader != writer);
|
|
|
|
/* Check the ends of the purported conflict first. */
|
|
if (SxactIsDoomed(reader)
|
|
|| SxactIsDoomed(writer)
|
|
|| SHMQueueEmpty(&reader->outConflicts)
|
|
|| SHMQueueEmpty(&writer->inConflicts))
|
|
return false;
|
|
|
|
/* A conflict is possible; walk the list to find out. */
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&reader->outConflicts,
|
|
&reader->outConflicts,
|
|
offsetof(RWConflictData, outLink));
|
|
while (conflict)
|
|
{
|
|
if (conflict->sxactIn == writer)
|
|
return true;
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&reader->outConflicts,
|
|
&conflict->outLink,
|
|
offsetof(RWConflictData, outLink));
|
|
}
|
|
|
|
/* No conflict found. */
|
|
return false;
|
|
}
|
|
|
|
static void
|
|
SetRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer)
|
|
{
|
|
RWConflict conflict;
|
|
|
|
Assert(reader != writer);
|
|
Assert(!RWConflictExists(reader, writer));
|
|
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&RWConflictPool->availableList,
|
|
&RWConflictPool->availableList,
|
|
offsetof(RWConflictData, outLink));
|
|
if (!conflict)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("not enough elements in RWConflictPool to record a read/write conflict"),
|
|
errhint("You might need to run fewer transactions at a time or increase max_connections.")));
|
|
|
|
SHMQueueDelete(&conflict->outLink);
|
|
|
|
conflict->sxactOut = reader;
|
|
conflict->sxactIn = writer;
|
|
SHMQueueInsertBefore(&reader->outConflicts, &conflict->outLink);
|
|
SHMQueueInsertBefore(&writer->inConflicts, &conflict->inLink);
|
|
}
|
|
|
|
static void
|
|
SetPossibleUnsafeConflict(SERIALIZABLEXACT *roXact,
|
|
SERIALIZABLEXACT *activeXact)
|
|
{
|
|
RWConflict conflict;
|
|
|
|
Assert(roXact != activeXact);
|
|
Assert(SxactIsReadOnly(roXact));
|
|
Assert(!SxactIsReadOnly(activeXact));
|
|
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&RWConflictPool->availableList,
|
|
&RWConflictPool->availableList,
|
|
offsetof(RWConflictData, outLink));
|
|
if (!conflict)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("not enough elements in RWConflictPool to record a potential read/write conflict"),
|
|
errhint("You might need to run fewer transactions at a time or increase max_connections.")));
|
|
|
|
SHMQueueDelete(&conflict->outLink);
|
|
|
|
conflict->sxactOut = activeXact;
|
|
conflict->sxactIn = roXact;
|
|
SHMQueueInsertBefore(&activeXact->possibleUnsafeConflicts,
|
|
&conflict->outLink);
|
|
SHMQueueInsertBefore(&roXact->possibleUnsafeConflicts,
|
|
&conflict->inLink);
|
|
}
|
|
|
|
static void
|
|
ReleaseRWConflict(RWConflict conflict)
|
|
{
|
|
SHMQueueDelete(&conflict->inLink);
|
|
SHMQueueDelete(&conflict->outLink);
|
|
SHMQueueInsertBefore(&RWConflictPool->availableList, &conflict->outLink);
|
|
}
|
|
|
|
static void
|
|
FlagSxactUnsafe(SERIALIZABLEXACT *sxact)
|
|
{
|
|
RWConflict conflict,
|
|
nextConflict;
|
|
|
|
Assert(SxactIsReadOnly(sxact));
|
|
Assert(!SxactIsROSafe(sxact));
|
|
|
|
sxact->flags |= SXACT_FLAG_RO_UNSAFE;
|
|
|
|
/*
|
|
* We know this isn't a safe snapshot, so we can stop looking for other
|
|
* potential conflicts.
|
|
*/
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&sxact->possibleUnsafeConflicts,
|
|
&sxact->possibleUnsafeConflicts,
|
|
offsetof(RWConflictData, inLink));
|
|
while (conflict)
|
|
{
|
|
nextConflict = (RWConflict)
|
|
SHMQueueNext(&sxact->possibleUnsafeConflicts,
|
|
&conflict->inLink,
|
|
offsetof(RWConflictData, inLink));
|
|
|
|
Assert(!SxactIsReadOnly(conflict->sxactOut));
|
|
Assert(sxact == conflict->sxactIn);
|
|
|
|
ReleaseRWConflict(conflict);
|
|
|
|
conflict = nextConflict;
|
|
}
|
|
}
|
|
|
|
/*------------------------------------------------------------------------*/
|
|
|
|
/*
|
|
* We will work on the page range of 0..OLDSERXID_MAX_PAGE.
|
|
* Compares using wraparound logic, as is required by slru.c.
|
|
*/
|
|
static bool
|
|
OldSerXidPagePrecedesLogically(int p, int q)
|
|
{
|
|
int diff;
|
|
|
|
/*
|
|
* We have to compare modulo (OLDSERXID_MAX_PAGE+1)/2. Both inputs should
|
|
* be in the range 0..OLDSERXID_MAX_PAGE.
|
|
*/
|
|
Assert(p >= 0 && p <= OLDSERXID_MAX_PAGE);
|
|
Assert(q >= 0 && q <= OLDSERXID_MAX_PAGE);
|
|
|
|
diff = p - q;
|
|
if (diff >= ((OLDSERXID_MAX_PAGE + 1) / 2))
|
|
diff -= OLDSERXID_MAX_PAGE + 1;
|
|
else if (diff < -((int) (OLDSERXID_MAX_PAGE + 1) / 2))
|
|
diff += OLDSERXID_MAX_PAGE + 1;
|
|
return diff < 0;
|
|
}
|
|
|
|
/*
|
|
* Initialize for the tracking of old serializable committed xids.
|
|
*/
|
|
static void
|
|
OldSerXidInit(void)
|
|
{
|
|
bool found;
|
|
|
|
/*
|
|
* Set up SLRU management of the pg_serial data.
|
|
*/
|
|
OldSerXidSlruCtl->PagePrecedes = OldSerXidPagePrecedesLogically;
|
|
SimpleLruInit(OldSerXidSlruCtl, "oldserxid",
|
|
NUM_OLDSERXID_BUFFERS, 0, OldSerXidLock, "pg_serial",
|
|
LWTRANCHE_OLDSERXID_BUFFERS);
|
|
/* Override default assumption that writes should be fsync'd */
|
|
OldSerXidSlruCtl->do_fsync = false;
|
|
|
|
/*
|
|
* Create or attach to the OldSerXidControl structure.
|
|
*/
|
|
oldSerXidControl = (OldSerXidControl)
|
|
ShmemInitStruct("OldSerXidControlData", sizeof(OldSerXidControlData), &found);
|
|
|
|
Assert(found == IsUnderPostmaster);
|
|
if (!found)
|
|
{
|
|
/*
|
|
* Set control information to reflect empty SLRU.
|
|
*/
|
|
oldSerXidControl->headPage = -1;
|
|
oldSerXidControl->headXid = InvalidTransactionId;
|
|
oldSerXidControl->tailXid = InvalidTransactionId;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Record a committed read write serializable xid and the minimum
|
|
* commitSeqNo of any transactions to which this xid had a rw-conflict out.
|
|
* An invalid seqNo means that there were no conflicts out from xid.
|
|
*/
|
|
static void
|
|
OldSerXidAdd(TransactionId xid, SerCommitSeqNo minConflictCommitSeqNo)
|
|
{
|
|
TransactionId tailXid;
|
|
int targetPage;
|
|
int slotno;
|
|
int firstZeroPage;
|
|
bool isNewPage;
|
|
|
|
Assert(TransactionIdIsValid(xid));
|
|
|
|
targetPage = OldSerXidPage(xid);
|
|
|
|
LWLockAcquire(OldSerXidLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* If no serializable transactions are active, there shouldn't be anything
|
|
* to push out to the SLRU. Hitting this assert would mean there's
|
|
* something wrong with the earlier cleanup logic.
|
|
*/
|
|
tailXid = oldSerXidControl->tailXid;
|
|
Assert(TransactionIdIsValid(tailXid));
|
|
|
|
/*
|
|
* If the SLRU is currently unused, zero out the whole active region from
|
|
* tailXid to headXid before taking it into use. Otherwise zero out only
|
|
* any new pages that enter the tailXid-headXid range as we advance
|
|
* headXid.
|
|
*/
|
|
if (oldSerXidControl->headPage < 0)
|
|
{
|
|
firstZeroPage = OldSerXidPage(tailXid);
|
|
isNewPage = true;
|
|
}
|
|
else
|
|
{
|
|
firstZeroPage = OldSerXidNextPage(oldSerXidControl->headPage);
|
|
isNewPage = OldSerXidPagePrecedesLogically(oldSerXidControl->headPage,
|
|
targetPage);
|
|
}
|
|
|
|
if (!TransactionIdIsValid(oldSerXidControl->headXid)
|
|
|| TransactionIdFollows(xid, oldSerXidControl->headXid))
|
|
oldSerXidControl->headXid = xid;
|
|
if (isNewPage)
|
|
oldSerXidControl->headPage = targetPage;
|
|
|
|
if (isNewPage)
|
|
{
|
|
/* Initialize intervening pages. */
|
|
while (firstZeroPage != targetPage)
|
|
{
|
|
(void) SimpleLruZeroPage(OldSerXidSlruCtl, firstZeroPage);
|
|
firstZeroPage = OldSerXidNextPage(firstZeroPage);
|
|
}
|
|
slotno = SimpleLruZeroPage(OldSerXidSlruCtl, targetPage);
|
|
}
|
|
else
|
|
slotno = SimpleLruReadPage(OldSerXidSlruCtl, targetPage, true, xid);
|
|
|
|
OldSerXidValue(slotno, xid) = minConflictCommitSeqNo;
|
|
OldSerXidSlruCtl->shared->page_dirty[slotno] = true;
|
|
|
|
LWLockRelease(OldSerXidLock);
|
|
}
|
|
|
|
/*
|
|
* Get the minimum commitSeqNo for any conflict out for the given xid. For
|
|
* a transaction which exists but has no conflict out, InvalidSerCommitSeqNo
|
|
* will be returned.
|
|
*/
|
|
static SerCommitSeqNo
|
|
OldSerXidGetMinConflictCommitSeqNo(TransactionId xid)
|
|
{
|
|
TransactionId headXid;
|
|
TransactionId tailXid;
|
|
SerCommitSeqNo val;
|
|
int slotno;
|
|
|
|
Assert(TransactionIdIsValid(xid));
|
|
|
|
LWLockAcquire(OldSerXidLock, LW_SHARED);
|
|
headXid = oldSerXidControl->headXid;
|
|
tailXid = oldSerXidControl->tailXid;
|
|
LWLockRelease(OldSerXidLock);
|
|
|
|
if (!TransactionIdIsValid(headXid))
|
|
return 0;
|
|
|
|
Assert(TransactionIdIsValid(tailXid));
|
|
|
|
if (TransactionIdPrecedes(xid, tailXid)
|
|
|| TransactionIdFollows(xid, headXid))
|
|
return 0;
|
|
|
|
/*
|
|
* The following function must be called without holding OldSerXidLock,
|
|
* but will return with that lock held, which must then be released.
|
|
*/
|
|
slotno = SimpleLruReadPage_ReadOnly(OldSerXidSlruCtl,
|
|
OldSerXidPage(xid), xid);
|
|
val = OldSerXidValue(slotno, xid);
|
|
LWLockRelease(OldSerXidLock);
|
|
return val;
|
|
}
|
|
|
|
/*
|
|
* Call this whenever there is a new xmin for active serializable
|
|
* transactions. We don't need to keep information on transactions which
|
|
* precede that. InvalidTransactionId means none active, so everything in
|
|
* the SLRU can be discarded.
|
|
*/
|
|
static void
|
|
OldSerXidSetActiveSerXmin(TransactionId xid)
|
|
{
|
|
LWLockAcquire(OldSerXidLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* When no sxacts are active, nothing overlaps, set the xid values to
|
|
* invalid to show that there are no valid entries. Don't clear headPage,
|
|
* though. A new xmin might still land on that page, and we don't want to
|
|
* repeatedly zero out the same page.
|
|
*/
|
|
if (!TransactionIdIsValid(xid))
|
|
{
|
|
oldSerXidControl->tailXid = InvalidTransactionId;
|
|
oldSerXidControl->headXid = InvalidTransactionId;
|
|
LWLockRelease(OldSerXidLock);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* When we're recovering prepared transactions, the global xmin might move
|
|
* backwards depending on the order they're recovered. Normally that's not
|
|
* OK, but during recovery no serializable transactions will commit, so
|
|
* the SLRU is empty and we can get away with it.
|
|
*/
|
|
if (RecoveryInProgress())
|
|
{
|
|
Assert(oldSerXidControl->headPage < 0);
|
|
if (!TransactionIdIsValid(oldSerXidControl->tailXid)
|
|
|| TransactionIdPrecedes(xid, oldSerXidControl->tailXid))
|
|
{
|
|
oldSerXidControl->tailXid = xid;
|
|
}
|
|
LWLockRelease(OldSerXidLock);
|
|
return;
|
|
}
|
|
|
|
Assert(!TransactionIdIsValid(oldSerXidControl->tailXid)
|
|
|| TransactionIdFollows(xid, oldSerXidControl->tailXid));
|
|
|
|
oldSerXidControl->tailXid = xid;
|
|
|
|
LWLockRelease(OldSerXidLock);
|
|
}
|
|
|
|
/*
|
|
* Perform a checkpoint --- either during shutdown, or on-the-fly
|
|
*
|
|
* We don't have any data that needs to survive a restart, but this is a
|
|
* convenient place to truncate the SLRU.
|
|
*/
|
|
void
|
|
CheckPointPredicate(void)
|
|
{
|
|
int tailPage;
|
|
|
|
LWLockAcquire(OldSerXidLock, LW_EXCLUSIVE);
|
|
|
|
/* Exit quickly if the SLRU is currently not in use. */
|
|
if (oldSerXidControl->headPage < 0)
|
|
{
|
|
LWLockRelease(OldSerXidLock);
|
|
return;
|
|
}
|
|
|
|
if (TransactionIdIsValid(oldSerXidControl->tailXid))
|
|
{
|
|
/* We can truncate the SLRU up to the page containing tailXid */
|
|
tailPage = OldSerXidPage(oldSerXidControl->tailXid);
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* The SLRU is no longer needed. Truncate to head before we set head
|
|
* invalid.
|
|
*
|
|
* XXX: It's possible that the SLRU is not needed again until XID
|
|
* wrap-around has happened, so that the segment containing headPage
|
|
* that we leave behind will appear to be new again. In that case it
|
|
* won't be removed until XID horizon advances enough to make it
|
|
* current again.
|
|
*/
|
|
tailPage = oldSerXidControl->headPage;
|
|
oldSerXidControl->headPage = -1;
|
|
}
|
|
|
|
LWLockRelease(OldSerXidLock);
|
|
|
|
/* Truncate away pages that are no longer required */
|
|
SimpleLruTruncate(OldSerXidSlruCtl, tailPage);
|
|
|
|
/*
|
|
* Flush dirty SLRU pages to disk
|
|
*
|
|
* This is not actually necessary from a correctness point of view. We do
|
|
* it merely as a debugging aid.
|
|
*
|
|
* We're doing this after the truncation to avoid writing pages right
|
|
* before deleting the file in which they sit, which would be completely
|
|
* pointless.
|
|
*/
|
|
SimpleLruFlush(OldSerXidSlruCtl, true);
|
|
}
|
|
|
|
/*------------------------------------------------------------------------*/
|
|
|
|
/*
|
|
* InitPredicateLocks -- Initialize the predicate locking data structures.
|
|
*
|
|
* This is called from CreateSharedMemoryAndSemaphores(), which see for
|
|
* more comments. In the normal postmaster case, the shared hash tables
|
|
* are created here. Backends inherit the pointers
|
|
* to the shared tables via fork(). In the EXEC_BACKEND case, each
|
|
* backend re-executes this code to obtain pointers to the already existing
|
|
* shared hash tables.
|
|
*/
|
|
void
|
|
InitPredicateLocks(void)
|
|
{
|
|
HASHCTL info;
|
|
long max_table_size;
|
|
Size requestSize;
|
|
bool found;
|
|
|
|
#ifndef EXEC_BACKEND
|
|
Assert(!IsUnderPostmaster);
|
|
#endif
|
|
|
|
/*
|
|
* Compute size of predicate lock target hashtable. Note these
|
|
* calculations must agree with PredicateLockShmemSize!
|
|
*/
|
|
max_table_size = NPREDICATELOCKTARGETENTS();
|
|
|
|
/*
|
|
* Allocate hash table for PREDICATELOCKTARGET structs. This stores
|
|
* per-predicate-lock-target information.
|
|
*/
|
|
MemSet(&info, 0, sizeof(info));
|
|
info.keysize = sizeof(PREDICATELOCKTARGETTAG);
|
|
info.entrysize = sizeof(PREDICATELOCKTARGET);
|
|
info.num_partitions = NUM_PREDICATELOCK_PARTITIONS;
|
|
|
|
PredicateLockTargetHash = ShmemInitHash("PREDICATELOCKTARGET hash",
|
|
max_table_size,
|
|
max_table_size,
|
|
&info,
|
|
HASH_ELEM | HASH_BLOBS |
|
|
HASH_PARTITION | HASH_FIXED_SIZE);
|
|
|
|
/*
|
|
* Reserve a dummy entry in the hash table; we use it to make sure there's
|
|
* always one entry available when we need to split or combine a page,
|
|
* because running out of space there could mean aborting a
|
|
* non-serializable transaction.
|
|
*/
|
|
if (!IsUnderPostmaster)
|
|
{
|
|
(void) hash_search(PredicateLockTargetHash, &ScratchTargetTag,
|
|
HASH_ENTER, &found);
|
|
Assert(!found);
|
|
}
|
|
|
|
/* Pre-calculate the hash and partition lock of the scratch entry */
|
|
ScratchTargetTagHash = PredicateLockTargetTagHashCode(&ScratchTargetTag);
|
|
ScratchPartitionLock = PredicateLockHashPartitionLock(ScratchTargetTagHash);
|
|
|
|
/*
|
|
* Allocate hash table for PREDICATELOCK structs. This stores per
|
|
* xact-lock-of-a-target information.
|
|
*/
|
|
MemSet(&info, 0, sizeof(info));
|
|
info.keysize = sizeof(PREDICATELOCKTAG);
|
|
info.entrysize = sizeof(PREDICATELOCK);
|
|
info.hash = predicatelock_hash;
|
|
info.num_partitions = NUM_PREDICATELOCK_PARTITIONS;
|
|
|
|
/* Assume an average of 2 xacts per target */
|
|
max_table_size *= 2;
|
|
|
|
PredicateLockHash = ShmemInitHash("PREDICATELOCK hash",
|
|
max_table_size,
|
|
max_table_size,
|
|
&info,
|
|
HASH_ELEM | HASH_FUNCTION |
|
|
HASH_PARTITION | HASH_FIXED_SIZE);
|
|
|
|
/*
|
|
* Compute size for serializable transaction hashtable. Note these
|
|
* calculations must agree with PredicateLockShmemSize!
|
|
*/
|
|
max_table_size = (MaxBackends + max_prepared_xacts);
|
|
|
|
/*
|
|
* Allocate a list to hold information on transactions participating in
|
|
* predicate locking.
|
|
*
|
|
* Assume an average of 10 predicate locking transactions per backend.
|
|
* This allows aggressive cleanup while detail is present before data must
|
|
* be summarized for storage in SLRU and the "dummy" transaction.
|
|
*/
|
|
max_table_size *= 10;
|
|
|
|
PredXact = ShmemInitStruct("PredXactList",
|
|
PredXactListDataSize,
|
|
&found);
|
|
Assert(found == IsUnderPostmaster);
|
|
if (!found)
|
|
{
|
|
int i;
|
|
|
|
SHMQueueInit(&PredXact->availableList);
|
|
SHMQueueInit(&PredXact->activeList);
|
|
PredXact->SxactGlobalXmin = InvalidTransactionId;
|
|
PredXact->SxactGlobalXminCount = 0;
|
|
PredXact->WritableSxactCount = 0;
|
|
PredXact->LastSxactCommitSeqNo = FirstNormalSerCommitSeqNo - 1;
|
|
PredXact->CanPartialClearThrough = 0;
|
|
PredXact->HavePartialClearedThrough = 0;
|
|
requestSize = mul_size((Size) max_table_size,
|
|
PredXactListElementDataSize);
|
|
PredXact->element = ShmemAlloc(requestSize);
|
|
/* Add all elements to available list, clean. */
|
|
memset(PredXact->element, 0, requestSize);
|
|
for (i = 0; i < max_table_size; i++)
|
|
{
|
|
LWLockInitialize(&PredXact->element[i].sxact.predicateLockListLock,
|
|
LWTRANCHE_SXACT);
|
|
SHMQueueInsertBefore(&(PredXact->availableList),
|
|
&(PredXact->element[i].link));
|
|
}
|
|
PredXact->OldCommittedSxact = CreatePredXact();
|
|
SetInvalidVirtualTransactionId(PredXact->OldCommittedSxact->vxid);
|
|
PredXact->OldCommittedSxact->prepareSeqNo = 0;
|
|
PredXact->OldCommittedSxact->commitSeqNo = 0;
|
|
PredXact->OldCommittedSxact->SeqNo.lastCommitBeforeSnapshot = 0;
|
|
SHMQueueInit(&PredXact->OldCommittedSxact->outConflicts);
|
|
SHMQueueInit(&PredXact->OldCommittedSxact->inConflicts);
|
|
SHMQueueInit(&PredXact->OldCommittedSxact->predicateLocks);
|
|
SHMQueueInit(&PredXact->OldCommittedSxact->finishedLink);
|
|
SHMQueueInit(&PredXact->OldCommittedSxact->possibleUnsafeConflicts);
|
|
PredXact->OldCommittedSxact->topXid = InvalidTransactionId;
|
|
PredXact->OldCommittedSxact->finishedBefore = InvalidTransactionId;
|
|
PredXact->OldCommittedSxact->xmin = InvalidTransactionId;
|
|
PredXact->OldCommittedSxact->flags = SXACT_FLAG_COMMITTED;
|
|
PredXact->OldCommittedSxact->pid = 0;
|
|
}
|
|
/* This never changes, so let's keep a local copy. */
|
|
OldCommittedSxact = PredXact->OldCommittedSxact;
|
|
|
|
/*
|
|
* Allocate hash table for SERIALIZABLEXID structs. This stores per-xid
|
|
* information for serializable transactions which have accessed data.
|
|
*/
|
|
MemSet(&info, 0, sizeof(info));
|
|
info.keysize = sizeof(SERIALIZABLEXIDTAG);
|
|
info.entrysize = sizeof(SERIALIZABLEXID);
|
|
|
|
SerializableXidHash = ShmemInitHash("SERIALIZABLEXID hash",
|
|
max_table_size,
|
|
max_table_size,
|
|
&info,
|
|
HASH_ELEM | HASH_BLOBS |
|
|
HASH_FIXED_SIZE);
|
|
|
|
/*
|
|
* Allocate space for tracking rw-conflicts in lists attached to the
|
|
* transactions.
|
|
*
|
|
* Assume an average of 5 conflicts per transaction. Calculations suggest
|
|
* that this will prevent resource exhaustion in even the most pessimal
|
|
* loads up to max_connections = 200 with all 200 connections pounding the
|
|
* database with serializable transactions. Beyond that, there may be
|
|
* occasional transactions canceled when trying to flag conflicts. That's
|
|
* probably OK.
|
|
*/
|
|
max_table_size *= 5;
|
|
|
|
RWConflictPool = ShmemInitStruct("RWConflictPool",
|
|
RWConflictPoolHeaderDataSize,
|
|
&found);
|
|
Assert(found == IsUnderPostmaster);
|
|
if (!found)
|
|
{
|
|
int i;
|
|
|
|
SHMQueueInit(&RWConflictPool->availableList);
|
|
requestSize = mul_size((Size) max_table_size,
|
|
RWConflictDataSize);
|
|
RWConflictPool->element = ShmemAlloc(requestSize);
|
|
/* Add all elements to available list, clean. */
|
|
memset(RWConflictPool->element, 0, requestSize);
|
|
for (i = 0; i < max_table_size; i++)
|
|
{
|
|
SHMQueueInsertBefore(&(RWConflictPool->availableList),
|
|
&(RWConflictPool->element[i].outLink));
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Create or attach to the header for the list of finished serializable
|
|
* transactions.
|
|
*/
|
|
FinishedSerializableTransactions = (SHM_QUEUE *)
|
|
ShmemInitStruct("FinishedSerializableTransactions",
|
|
sizeof(SHM_QUEUE),
|
|
&found);
|
|
Assert(found == IsUnderPostmaster);
|
|
if (!found)
|
|
SHMQueueInit(FinishedSerializableTransactions);
|
|
|
|
/*
|
|
* Initialize the SLRU storage for old committed serializable
|
|
* transactions.
|
|
*/
|
|
OldSerXidInit();
|
|
}
|
|
|
|
/*
|
|
* Estimate shared-memory space used for predicate lock table
|
|
*/
|
|
Size
|
|
PredicateLockShmemSize(void)
|
|
{
|
|
Size size = 0;
|
|
long max_table_size;
|
|
|
|
/* predicate lock target hash table */
|
|
max_table_size = NPREDICATELOCKTARGETENTS();
|
|
size = add_size(size, hash_estimate_size(max_table_size,
|
|
sizeof(PREDICATELOCKTARGET)));
|
|
|
|
/* predicate lock hash table */
|
|
max_table_size *= 2;
|
|
size = add_size(size, hash_estimate_size(max_table_size,
|
|
sizeof(PREDICATELOCK)));
|
|
|
|
/*
|
|
* Since NPREDICATELOCKTARGETENTS is only an estimate, add 10% safety
|
|
* margin.
|
|
*/
|
|
size = add_size(size, size / 10);
|
|
|
|
/* transaction list */
|
|
max_table_size = MaxBackends + max_prepared_xacts;
|
|
max_table_size *= 10;
|
|
size = add_size(size, PredXactListDataSize);
|
|
size = add_size(size, mul_size((Size) max_table_size,
|
|
PredXactListElementDataSize));
|
|
|
|
/* transaction xid table */
|
|
size = add_size(size, hash_estimate_size(max_table_size,
|
|
sizeof(SERIALIZABLEXID)));
|
|
|
|
/* rw-conflict pool */
|
|
max_table_size *= 5;
|
|
size = add_size(size, RWConflictPoolHeaderDataSize);
|
|
size = add_size(size, mul_size((Size) max_table_size,
|
|
RWConflictDataSize));
|
|
|
|
/* Head for list of finished serializable transactions. */
|
|
size = add_size(size, sizeof(SHM_QUEUE));
|
|
|
|
/* Shared memory structures for SLRU tracking of old committed xids. */
|
|
size = add_size(size, sizeof(OldSerXidControlData));
|
|
size = add_size(size, SimpleLruShmemSize(NUM_OLDSERXID_BUFFERS, 0));
|
|
|
|
return size;
|
|
}
|
|
|
|
|
|
/*
|
|
* Compute the hash code associated with a PREDICATELOCKTAG.
|
|
*
|
|
* Because we want to use just one set of partition locks for both the
|
|
* PREDICATELOCKTARGET and PREDICATELOCK hash tables, we have to make sure
|
|
* that PREDICATELOCKs fall into the same partition number as their
|
|
* associated PREDICATELOCKTARGETs. dynahash.c expects the partition number
|
|
* to be the low-order bits of the hash code, and therefore a
|
|
* PREDICATELOCKTAG's hash code must have the same low-order bits as the
|
|
* associated PREDICATELOCKTARGETTAG's hash code. We achieve this with this
|
|
* specialized hash function.
|
|
*/
|
|
static uint32
|
|
predicatelock_hash(const void *key, Size keysize)
|
|
{
|
|
const PREDICATELOCKTAG *predicatelocktag = (const PREDICATELOCKTAG *) key;
|
|
uint32 targethash;
|
|
|
|
Assert(keysize == sizeof(PREDICATELOCKTAG));
|
|
|
|
/* Look into the associated target object, and compute its hash code */
|
|
targethash = PredicateLockTargetTagHashCode(&predicatelocktag->myTarget->tag);
|
|
|
|
return PredicateLockHashCodeFromTargetHashCode(predicatelocktag, targethash);
|
|
}
|
|
|
|
|
|
/*
|
|
* GetPredicateLockStatusData
|
|
* Return a table containing the internal state of the predicate
|
|
* lock manager for use in pg_lock_status.
|
|
*
|
|
* Like GetLockStatusData, this function tries to hold the partition LWLocks
|
|
* for as short a time as possible by returning two arrays that simply
|
|
* contain the PREDICATELOCKTARGETTAG and SERIALIZABLEXACT for each lock
|
|
* table entry. Multiple copies of the same PREDICATELOCKTARGETTAG and
|
|
* SERIALIZABLEXACT will likely appear.
|
|
*/
|
|
PredicateLockData *
|
|
GetPredicateLockStatusData(void)
|
|
{
|
|
PredicateLockData *data;
|
|
int i;
|
|
int els,
|
|
el;
|
|
HASH_SEQ_STATUS seqstat;
|
|
PREDICATELOCK *predlock;
|
|
|
|
data = (PredicateLockData *) palloc(sizeof(PredicateLockData));
|
|
|
|
/*
|
|
* To ensure consistency, take simultaneous locks on all partition locks
|
|
* in ascending order, then SerializableXactHashLock.
|
|
*/
|
|
for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++)
|
|
LWLockAcquire(PredicateLockHashPartitionLockByIndex(i), LW_SHARED);
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
|
|
/* Get number of locks and allocate appropriately-sized arrays. */
|
|
els = hash_get_num_entries(PredicateLockHash);
|
|
data->nelements = els;
|
|
data->locktags = (PREDICATELOCKTARGETTAG *)
|
|
palloc(sizeof(PREDICATELOCKTARGETTAG) * els);
|
|
data->xacts = (SERIALIZABLEXACT *)
|
|
palloc(sizeof(SERIALIZABLEXACT) * els);
|
|
|
|
|
|
/* Scan through PredicateLockHash and copy contents */
|
|
hash_seq_init(&seqstat, PredicateLockHash);
|
|
|
|
el = 0;
|
|
|
|
while ((predlock = (PREDICATELOCK *) hash_seq_search(&seqstat)))
|
|
{
|
|
data->locktags[el] = predlock->tag.myTarget->tag;
|
|
data->xacts[el] = *predlock->tag.myXact;
|
|
el++;
|
|
}
|
|
|
|
Assert(el == els);
|
|
|
|
/* Release locks in reverse order */
|
|
LWLockRelease(SerializableXactHashLock);
|
|
for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--)
|
|
LWLockRelease(PredicateLockHashPartitionLockByIndex(i));
|
|
|
|
return data;
|
|
}
|
|
|
|
/*
|
|
* Free up shared memory structures by pushing the oldest sxact (the one at
|
|
* the front of the SummarizeOldestCommittedSxact queue) into summary form.
|
|
* Each call will free exactly one SERIALIZABLEXACT structure and may also
|
|
* free one or more of these structures: SERIALIZABLEXID, PREDICATELOCK,
|
|
* PREDICATELOCKTARGET, RWConflictData.
|
|
*/
|
|
static void
|
|
SummarizeOldestCommittedSxact(void)
|
|
{
|
|
SERIALIZABLEXACT *sxact;
|
|
|
|
LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* This function is only called if there are no sxact slots available.
|
|
* Some of them must belong to old, already-finished transactions, so
|
|
* there should be something in FinishedSerializableTransactions list that
|
|
* we can summarize. However, there's a race condition: while we were not
|
|
* holding any locks, a transaction might have ended and cleaned up all
|
|
* the finished sxact entries already, freeing up their sxact slots. In
|
|
* that case, we have nothing to do here. The caller will find one of the
|
|
* slots released by the other backend when it retries.
|
|
*/
|
|
if (SHMQueueEmpty(FinishedSerializableTransactions))
|
|
{
|
|
LWLockRelease(SerializableFinishedListLock);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Grab the first sxact off the finished list -- this will be the earliest
|
|
* commit. Remove it from the list.
|
|
*/
|
|
sxact = (SERIALIZABLEXACT *)
|
|
SHMQueueNext(FinishedSerializableTransactions,
|
|
FinishedSerializableTransactions,
|
|
offsetof(SERIALIZABLEXACT, finishedLink));
|
|
SHMQueueDelete(&(sxact->finishedLink));
|
|
|
|
/* Add to SLRU summary information. */
|
|
if (TransactionIdIsValid(sxact->topXid) && !SxactIsReadOnly(sxact))
|
|
OldSerXidAdd(sxact->topXid, SxactHasConflictOut(sxact)
|
|
? sxact->SeqNo.earliestOutConflictCommit : InvalidSerCommitSeqNo);
|
|
|
|
/* Summarize and release the detail. */
|
|
ReleaseOneSerializableXact(sxact, false, true);
|
|
|
|
LWLockRelease(SerializableFinishedListLock);
|
|
}
|
|
|
|
/*
|
|
* GetSafeSnapshot
|
|
* Obtain and register a snapshot for a READ ONLY DEFERRABLE
|
|
* transaction. Ensures that the snapshot is "safe", i.e. a
|
|
* read-only transaction running on it can execute serializably
|
|
* without further checks. This requires waiting for concurrent
|
|
* transactions to complete, and retrying with a new snapshot if
|
|
* one of them could possibly create a conflict.
|
|
*
|
|
* As with GetSerializableTransactionSnapshot (which this is a subroutine
|
|
* for), the passed-in Snapshot pointer should reference a static data
|
|
* area that can safely be passed to GetSnapshotData.
|
|
*/
|
|
static Snapshot
|
|
GetSafeSnapshot(Snapshot origSnapshot)
|
|
{
|
|
Snapshot snapshot;
|
|
|
|
Assert(XactReadOnly && XactDeferrable);
|
|
|
|
while (true)
|
|
{
|
|
/*
|
|
* GetSerializableTransactionSnapshotInt is going to call
|
|
* GetSnapshotData, so we need to provide it the static snapshot area
|
|
* our caller passed to us. The pointer returned is actually the same
|
|
* one passed to it, but we avoid assuming that here.
|
|
*/
|
|
snapshot = GetSerializableTransactionSnapshotInt(origSnapshot,
|
|
NULL, InvalidPid);
|
|
|
|
if (MySerializableXact == InvalidSerializableXact)
|
|
return snapshot; /* no concurrent r/w xacts; it's safe */
|
|
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Wait for concurrent transactions to finish. Stop early if one of
|
|
* them marked us as conflicted.
|
|
*/
|
|
MySerializableXact->flags |= SXACT_FLAG_DEFERRABLE_WAITING;
|
|
while (!(SHMQueueEmpty(&MySerializableXact->possibleUnsafeConflicts) ||
|
|
SxactIsROUnsafe(MySerializableXact)))
|
|
{
|
|
LWLockRelease(SerializableXactHashLock);
|
|
ProcWaitForSignal(WAIT_EVENT_SAFE_SNAPSHOT);
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
}
|
|
MySerializableXact->flags &= ~SXACT_FLAG_DEFERRABLE_WAITING;
|
|
|
|
if (!SxactIsROUnsafe(MySerializableXact))
|
|
{
|
|
LWLockRelease(SerializableXactHashLock);
|
|
break; /* success */
|
|
}
|
|
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
/* else, need to retry... */
|
|
ereport(DEBUG2,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("deferrable snapshot was unsafe; trying a new one")));
|
|
ReleasePredicateLocks(false, false);
|
|
}
|
|
|
|
/*
|
|
* Now we have a safe snapshot, so we don't need to do any further checks.
|
|
*/
|
|
Assert(SxactIsROSafe(MySerializableXact));
|
|
ReleasePredicateLocks(false, true);
|
|
|
|
return snapshot;
|
|
}
|
|
|
|
/*
|
|
* GetSafeSnapshotBlockingPids
|
|
* If the specified process is currently blocked in GetSafeSnapshot,
|
|
* write the process IDs of all processes that it is blocked by
|
|
* into the caller-supplied buffer output[]. The list is truncated at
|
|
* output_size, and the number of PIDs written into the buffer is
|
|
* returned. Returns zero if the given PID is not currently blocked
|
|
* in GetSafeSnapshot.
|
|
*/
|
|
int
|
|
GetSafeSnapshotBlockingPids(int blocked_pid, int *output, int output_size)
|
|
{
|
|
int num_written = 0;
|
|
SERIALIZABLEXACT *sxact;
|
|
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
|
|
/* Find blocked_pid's SERIALIZABLEXACT by linear search. */
|
|
for (sxact = FirstPredXact(); sxact != NULL; sxact = NextPredXact(sxact))
|
|
{
|
|
if (sxact->pid == blocked_pid)
|
|
break;
|
|
}
|
|
|
|
/* Did we find it, and is it currently waiting in GetSafeSnapshot? */
|
|
if (sxact != NULL && SxactIsDeferrableWaiting(sxact))
|
|
{
|
|
RWConflict possibleUnsafeConflict;
|
|
|
|
/* Traverse the list of possible unsafe conflicts collecting PIDs. */
|
|
possibleUnsafeConflict = (RWConflict)
|
|
SHMQueueNext(&sxact->possibleUnsafeConflicts,
|
|
&sxact->possibleUnsafeConflicts,
|
|
offsetof(RWConflictData, inLink));
|
|
|
|
while (possibleUnsafeConflict != NULL && num_written < output_size)
|
|
{
|
|
output[num_written++] = possibleUnsafeConflict->sxactOut->pid;
|
|
possibleUnsafeConflict = (RWConflict)
|
|
SHMQueueNext(&sxact->possibleUnsafeConflicts,
|
|
&possibleUnsafeConflict->inLink,
|
|
offsetof(RWConflictData, inLink));
|
|
}
|
|
}
|
|
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
return num_written;
|
|
}
|
|
|
|
/*
|
|
* Acquire a snapshot that can be used for the current transaction.
|
|
*
|
|
* Make sure we have a SERIALIZABLEXACT reference in MySerializableXact.
|
|
* It should be current for this process and be contained in PredXact.
|
|
*
|
|
* The passed-in Snapshot pointer should reference a static data area that
|
|
* can safely be passed to GetSnapshotData. The return value is actually
|
|
* always this same pointer; no new snapshot data structure is allocated
|
|
* within this function.
|
|
*/
|
|
Snapshot
|
|
GetSerializableTransactionSnapshot(Snapshot snapshot)
|
|
{
|
|
Assert(IsolationIsSerializable());
|
|
|
|
/*
|
|
* Can't use serializable mode while recovery is still active, as it is,
|
|
* for example, on a hot standby. We could get here despite the check in
|
|
* check_XactIsoLevel() if default_transaction_isolation is set to
|
|
* serializable, so phrase the hint accordingly.
|
|
*/
|
|
if (RecoveryInProgress())
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
|
|
errmsg("cannot use serializable mode in a hot standby"),
|
|
errdetail("\"default_transaction_isolation\" is set to \"serializable\"."),
|
|
errhint("You can use \"SET default_transaction_isolation = 'repeatable read'\" to change the default.")));
|
|
|
|
/*
|
|
* A special optimization is available for SERIALIZABLE READ ONLY
|
|
* DEFERRABLE transactions -- we can wait for a suitable snapshot and
|
|
* thereby avoid all SSI overhead once it's running.
|
|
*/
|
|
if (XactReadOnly && XactDeferrable)
|
|
return GetSafeSnapshot(snapshot);
|
|
|
|
return GetSerializableTransactionSnapshotInt(snapshot,
|
|
NULL, InvalidPid);
|
|
}
|
|
|
|
/*
|
|
* Import a snapshot to be used for the current transaction.
|
|
*
|
|
* This is nearly the same as GetSerializableTransactionSnapshot, except that
|
|
* we don't take a new snapshot, but rather use the data we're handed.
|
|
*
|
|
* The caller must have verified that the snapshot came from a serializable
|
|
* transaction; and if we're read-write, the source transaction must not be
|
|
* read-only.
|
|
*/
|
|
void
|
|
SetSerializableTransactionSnapshot(Snapshot snapshot,
|
|
VirtualTransactionId *sourcevxid,
|
|
int sourcepid)
|
|
{
|
|
Assert(IsolationIsSerializable());
|
|
|
|
/*
|
|
* If this is called by parallel.c in a parallel worker, we don't want to
|
|
* create a SERIALIZABLEXACT just yet because the leader's
|
|
* SERIALIZABLEXACT will be installed with AttachSerializableXact(). We
|
|
* also don't want to reject SERIALIZABLE READ ONLY DEFERRABLE in this
|
|
* case, because the leader has already determined that the snapshot it
|
|
* has passed us is safe. So there is nothing for us to do.
|
|
*/
|
|
if (IsParallelWorker())
|
|
return;
|
|
|
|
/*
|
|
* We do not allow SERIALIZABLE READ ONLY DEFERRABLE transactions to
|
|
* import snapshots, since there's no way to wait for a safe snapshot when
|
|
* we're using the snap we're told to. (XXX instead of throwing an error,
|
|
* we could just ignore the XactDeferrable flag?)
|
|
*/
|
|
if (XactReadOnly && XactDeferrable)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
|
|
errmsg("a snapshot-importing transaction must not be READ ONLY DEFERRABLE")));
|
|
|
|
(void) GetSerializableTransactionSnapshotInt(snapshot, sourcevxid,
|
|
sourcepid);
|
|
}
|
|
|
|
/*
|
|
* Guts of GetSerializableTransactionSnapshot
|
|
*
|
|
* If sourcexid is valid, this is actually an import operation and we should
|
|
* skip calling GetSnapshotData, because the snapshot contents are already
|
|
* loaded up. HOWEVER: to avoid race conditions, we must check that the
|
|
* source xact is still running after we acquire SerializableXactHashLock.
|
|
* We do that by calling ProcArrayInstallImportedXmin.
|
|
*/
|
|
static Snapshot
|
|
GetSerializableTransactionSnapshotInt(Snapshot snapshot,
|
|
VirtualTransactionId *sourcevxid,
|
|
int sourcepid)
|
|
{
|
|
PGPROC *proc;
|
|
VirtualTransactionId vxid;
|
|
SERIALIZABLEXACT *sxact,
|
|
*othersxact;
|
|
|
|
/* We only do this for serializable transactions. Once. */
|
|
Assert(MySerializableXact == InvalidSerializableXact);
|
|
|
|
Assert(!RecoveryInProgress());
|
|
|
|
/*
|
|
* Since all parts of a serializable transaction must use the same
|
|
* snapshot, it is too late to establish one after a parallel operation
|
|
* has begun.
|
|
*/
|
|
if (IsInParallelMode())
|
|
elog(ERROR, "cannot establish serializable snapshot during a parallel operation");
|
|
|
|
proc = MyProc;
|
|
Assert(proc != NULL);
|
|
GET_VXID_FROM_PGPROC(vxid, *proc);
|
|
|
|
/*
|
|
* First we get the sxact structure, which may involve looping and access
|
|
* to the "finished" list to free a structure for use.
|
|
*
|
|
* We must hold SerializableXactHashLock when taking/checking the snapshot
|
|
* to avoid race conditions, for much the same reasons that
|
|
* GetSnapshotData takes the ProcArrayLock. Since we might have to
|
|
* release SerializableXactHashLock to call SummarizeOldestCommittedSxact,
|
|
* this means we have to create the sxact first, which is a bit annoying
|
|
* (in particular, an elog(ERROR) in procarray.c would cause us to leak
|
|
* the sxact). Consider refactoring to avoid this.
|
|
*/
|
|
#ifdef TEST_OLDSERXID
|
|
SummarizeOldestCommittedSxact();
|
|
#endif
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
do
|
|
{
|
|
sxact = CreatePredXact();
|
|
/* If null, push out committed sxact to SLRU summary & retry. */
|
|
if (!sxact)
|
|
{
|
|
LWLockRelease(SerializableXactHashLock);
|
|
SummarizeOldestCommittedSxact();
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
}
|
|
} while (!sxact);
|
|
|
|
/* Get the snapshot, or check that it's safe to use */
|
|
if (!sourcevxid)
|
|
snapshot = GetSnapshotData(snapshot);
|
|
else if (!ProcArrayInstallImportedXmin(snapshot->xmin, sourcevxid))
|
|
{
|
|
ReleasePredXact(sxact);
|
|
LWLockRelease(SerializableXactHashLock);
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
|
|
errmsg("could not import the requested snapshot"),
|
|
errdetail("The source process with PID %d is not running anymore.",
|
|
sourcepid)));
|
|
}
|
|
|
|
/*
|
|
* If there are no serializable transactions which are not read-only, we
|
|
* can "opt out" of predicate locking and conflict checking for a
|
|
* read-only transaction.
|
|
*
|
|
* The reason this is safe is that a read-only transaction can only become
|
|
* part of a dangerous structure if it overlaps a writable transaction
|
|
* which in turn overlaps a writable transaction which committed before
|
|
* the read-only transaction started. A new writable transaction can
|
|
* overlap this one, but it can't meet the other condition of overlapping
|
|
* a transaction which committed before this one started.
|
|
*/
|
|
if (XactReadOnly && PredXact->WritableSxactCount == 0)
|
|
{
|
|
ReleasePredXact(sxact);
|
|
LWLockRelease(SerializableXactHashLock);
|
|
return snapshot;
|
|
}
|
|
|
|
/* Maintain serializable global xmin info. */
|
|
if (!TransactionIdIsValid(PredXact->SxactGlobalXmin))
|
|
{
|
|
Assert(PredXact->SxactGlobalXminCount == 0);
|
|
PredXact->SxactGlobalXmin = snapshot->xmin;
|
|
PredXact->SxactGlobalXminCount = 1;
|
|
OldSerXidSetActiveSerXmin(snapshot->xmin);
|
|
}
|
|
else if (TransactionIdEquals(snapshot->xmin, PredXact->SxactGlobalXmin))
|
|
{
|
|
Assert(PredXact->SxactGlobalXminCount > 0);
|
|
PredXact->SxactGlobalXminCount++;
|
|
}
|
|
else
|
|
{
|
|
Assert(TransactionIdFollows(snapshot->xmin, PredXact->SxactGlobalXmin));
|
|
}
|
|
|
|
/* Initialize the structure. */
|
|
sxact->vxid = vxid;
|
|
sxact->SeqNo.lastCommitBeforeSnapshot = PredXact->LastSxactCommitSeqNo;
|
|
sxact->prepareSeqNo = InvalidSerCommitSeqNo;
|
|
sxact->commitSeqNo = InvalidSerCommitSeqNo;
|
|
SHMQueueInit(&(sxact->outConflicts));
|
|
SHMQueueInit(&(sxact->inConflicts));
|
|
SHMQueueInit(&(sxact->possibleUnsafeConflicts));
|
|
sxact->topXid = GetTopTransactionIdIfAny();
|
|
sxact->finishedBefore = InvalidTransactionId;
|
|
sxact->xmin = snapshot->xmin;
|
|
sxact->pid = MyProcPid;
|
|
SHMQueueInit(&(sxact->predicateLocks));
|
|
SHMQueueElemInit(&(sxact->finishedLink));
|
|
sxact->flags = 0;
|
|
if (XactReadOnly)
|
|
{
|
|
sxact->flags |= SXACT_FLAG_READ_ONLY;
|
|
|
|
/*
|
|
* Register all concurrent r/w transactions as possible conflicts; if
|
|
* all of them commit without any outgoing conflicts to earlier
|
|
* transactions then this snapshot can be deemed safe (and we can run
|
|
* without tracking predicate locks).
|
|
*/
|
|
for (othersxact = FirstPredXact();
|
|
othersxact != NULL;
|
|
othersxact = NextPredXact(othersxact))
|
|
{
|
|
if (!SxactIsCommitted(othersxact)
|
|
&& !SxactIsDoomed(othersxact)
|
|
&& !SxactIsReadOnly(othersxact))
|
|
{
|
|
SetPossibleUnsafeConflict(sxact, othersxact);
|
|
}
|
|
}
|
|
}
|
|
else
|
|
{
|
|
++(PredXact->WritableSxactCount);
|
|
Assert(PredXact->WritableSxactCount <=
|
|
(MaxBackends + max_prepared_xacts));
|
|
}
|
|
|
|
MySerializableXact = sxact;
|
|
MyXactDidWrite = false; /* haven't written anything yet */
|
|
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
CreateLocalPredicateLockHash();
|
|
|
|
return snapshot;
|
|
}
|
|
|
|
static void
|
|
CreateLocalPredicateLockHash(void)
|
|
{
|
|
HASHCTL hash_ctl;
|
|
|
|
/* Initialize the backend-local hash table of parent locks */
|
|
Assert(LocalPredicateLockHash == NULL);
|
|
MemSet(&hash_ctl, 0, sizeof(hash_ctl));
|
|
hash_ctl.keysize = sizeof(PREDICATELOCKTARGETTAG);
|
|
hash_ctl.entrysize = sizeof(LOCALPREDICATELOCK);
|
|
LocalPredicateLockHash = hash_create("Local predicate lock",
|
|
max_predicate_locks_per_xact,
|
|
&hash_ctl,
|
|
HASH_ELEM | HASH_BLOBS);
|
|
}
|
|
|
|
/*
|
|
* Register the top level XID in SerializableXidHash.
|
|
* Also store it for easy reference in MySerializableXact.
|
|
*/
|
|
void
|
|
RegisterPredicateLockingXid(TransactionId xid)
|
|
{
|
|
SERIALIZABLEXIDTAG sxidtag;
|
|
SERIALIZABLEXID *sxid;
|
|
bool found;
|
|
|
|
/*
|
|
* If we're not tracking predicate lock data for this transaction, we
|
|
* should ignore the request and return quickly.
|
|
*/
|
|
if (MySerializableXact == InvalidSerializableXact)
|
|
return;
|
|
|
|
/* We should have a valid XID and be at the top level. */
|
|
Assert(TransactionIdIsValid(xid));
|
|
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
|
|
/* This should only be done once per transaction. */
|
|
Assert(MySerializableXact->topXid == InvalidTransactionId);
|
|
|
|
MySerializableXact->topXid = xid;
|
|
|
|
sxidtag.xid = xid;
|
|
sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash,
|
|
&sxidtag,
|
|
HASH_ENTER, &found);
|
|
Assert(!found);
|
|
|
|
/* Initialize the structure. */
|
|
sxid->myXact = MySerializableXact;
|
|
LWLockRelease(SerializableXactHashLock);
|
|
}
|
|
|
|
|
|
/*
|
|
* Check whether there are any predicate locks held by any transaction
|
|
* for the page at the given block number.
|
|
*
|
|
* Note that the transaction may be completed but not yet subject to
|
|
* cleanup due to overlapping serializable transactions. This must
|
|
* return valid information regardless of transaction isolation level.
|
|
*
|
|
* Also note that this doesn't check for a conflicting relation lock,
|
|
* just a lock specifically on the given page.
|
|
*
|
|
* One use is to support proper behavior during GiST index vacuum.
|
|
*/
|
|
bool
|
|
PageIsPredicateLocked(Relation relation, BlockNumber blkno)
|
|
{
|
|
PREDICATELOCKTARGETTAG targettag;
|
|
uint32 targettaghash;
|
|
LWLock *partitionLock;
|
|
PREDICATELOCKTARGET *target;
|
|
|
|
SET_PREDICATELOCKTARGETTAG_PAGE(targettag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id,
|
|
blkno);
|
|
|
|
targettaghash = PredicateLockTargetTagHashCode(&targettag);
|
|
partitionLock = PredicateLockHashPartitionLock(targettaghash);
|
|
LWLockAcquire(partitionLock, LW_SHARED);
|
|
target = (PREDICATELOCKTARGET *)
|
|
hash_search_with_hash_value(PredicateLockTargetHash,
|
|
&targettag, targettaghash,
|
|
HASH_FIND, NULL);
|
|
LWLockRelease(partitionLock);
|
|
|
|
return (target != NULL);
|
|
}
|
|
|
|
|
|
/*
|
|
* Check whether a particular lock is held by this transaction.
|
|
*
|
|
* Important note: this function may return false even if the lock is
|
|
* being held, because it uses the local lock table which is not
|
|
* updated if another transaction modifies our lock list (e.g. to
|
|
* split an index page). It can also return true when a coarser
|
|
* granularity lock that covers this target is being held. Be careful
|
|
* to only use this function in circumstances where such errors are
|
|
* acceptable!
|
|
*/
|
|
static bool
|
|
PredicateLockExists(const PREDICATELOCKTARGETTAG *targettag)
|
|
{
|
|
LOCALPREDICATELOCK *lock;
|
|
|
|
/* check local hash table */
|
|
lock = (LOCALPREDICATELOCK *) hash_search(LocalPredicateLockHash,
|
|
targettag,
|
|
HASH_FIND, NULL);
|
|
|
|
if (!lock)
|
|
return false;
|
|
|
|
/*
|
|
* Found entry in the table, but still need to check whether it's actually
|
|
* held -- it could just be a parent of some held lock.
|
|
*/
|
|
return lock->held;
|
|
}
|
|
|
|
/*
|
|
* Return the parent lock tag in the lock hierarchy: the next coarser
|
|
* lock that covers the provided tag.
|
|
*
|
|
* Returns true and sets *parent to the parent tag if one exists,
|
|
* returns false if none exists.
|
|
*/
|
|
static bool
|
|
GetParentPredicateLockTag(const PREDICATELOCKTARGETTAG *tag,
|
|
PREDICATELOCKTARGETTAG *parent)
|
|
{
|
|
switch (GET_PREDICATELOCKTARGETTAG_TYPE(*tag))
|
|
{
|
|
case PREDLOCKTAG_RELATION:
|
|
/* relation locks have no parent lock */
|
|
return false;
|
|
|
|
case PREDLOCKTAG_PAGE:
|
|
/* parent lock is relation lock */
|
|
SET_PREDICATELOCKTARGETTAG_RELATION(*parent,
|
|
GET_PREDICATELOCKTARGETTAG_DB(*tag),
|
|
GET_PREDICATELOCKTARGETTAG_RELATION(*tag));
|
|
|
|
return true;
|
|
|
|
case PREDLOCKTAG_TUPLE:
|
|
/* parent lock is page lock */
|
|
SET_PREDICATELOCKTARGETTAG_PAGE(*parent,
|
|
GET_PREDICATELOCKTARGETTAG_DB(*tag),
|
|
GET_PREDICATELOCKTARGETTAG_RELATION(*tag),
|
|
GET_PREDICATELOCKTARGETTAG_PAGE(*tag));
|
|
return true;
|
|
}
|
|
|
|
/* not reachable */
|
|
Assert(false);
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Check whether the lock we are considering is already covered by a
|
|
* coarser lock for our transaction.
|
|
*
|
|
* Like PredicateLockExists, this function might return a false
|
|
* negative, but it will never return a false positive.
|
|
*/
|
|
static bool
|
|
CoarserLockCovers(const PREDICATELOCKTARGETTAG *newtargettag)
|
|
{
|
|
PREDICATELOCKTARGETTAG targettag,
|
|
parenttag;
|
|
|
|
targettag = *newtargettag;
|
|
|
|
/* check parents iteratively until no more */
|
|
while (GetParentPredicateLockTag(&targettag, &parenttag))
|
|
{
|
|
targettag = parenttag;
|
|
if (PredicateLockExists(&targettag))
|
|
return true;
|
|
}
|
|
|
|
/* no more parents to check; lock is not covered */
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Remove the dummy entry from the predicate lock target hash, to free up some
|
|
* scratch space. The caller must be holding SerializablePredicateLockListLock,
|
|
* and must restore the entry with RestoreScratchTarget() before releasing the
|
|
* lock.
|
|
*
|
|
* If lockheld is true, the caller is already holding the partition lock
|
|
* of the partition containing the scratch entry.
|
|
*/
|
|
static void
|
|
RemoveScratchTarget(bool lockheld)
|
|
{
|
|
bool found;
|
|
|
|
Assert(LWLockHeldByMe(SerializablePredicateLockListLock));
|
|
|
|
if (!lockheld)
|
|
LWLockAcquire(ScratchPartitionLock, LW_EXCLUSIVE);
|
|
hash_search_with_hash_value(PredicateLockTargetHash,
|
|
&ScratchTargetTag,
|
|
ScratchTargetTagHash,
|
|
HASH_REMOVE, &found);
|
|
Assert(found);
|
|
if (!lockheld)
|
|
LWLockRelease(ScratchPartitionLock);
|
|
}
|
|
|
|
/*
|
|
* Re-insert the dummy entry in predicate lock target hash.
|
|
*/
|
|
static void
|
|
RestoreScratchTarget(bool lockheld)
|
|
{
|
|
bool found;
|
|
|
|
Assert(LWLockHeldByMe(SerializablePredicateLockListLock));
|
|
|
|
if (!lockheld)
|
|
LWLockAcquire(ScratchPartitionLock, LW_EXCLUSIVE);
|
|
hash_search_with_hash_value(PredicateLockTargetHash,
|
|
&ScratchTargetTag,
|
|
ScratchTargetTagHash,
|
|
HASH_ENTER, &found);
|
|
Assert(!found);
|
|
if (!lockheld)
|
|
LWLockRelease(ScratchPartitionLock);
|
|
}
|
|
|
|
/*
|
|
* Check whether the list of related predicate locks is empty for a
|
|
* predicate lock target, and remove the target if it is.
|
|
*/
|
|
static void
|
|
RemoveTargetIfNoLongerUsed(PREDICATELOCKTARGET *target, uint32 targettaghash)
|
|
{
|
|
PREDICATELOCKTARGET *rmtarget PG_USED_FOR_ASSERTS_ONLY;
|
|
|
|
Assert(LWLockHeldByMe(SerializablePredicateLockListLock));
|
|
|
|
/* Can't remove it until no locks at this target. */
|
|
if (!SHMQueueEmpty(&target->predicateLocks))
|
|
return;
|
|
|
|
/* Actually remove the target. */
|
|
rmtarget = hash_search_with_hash_value(PredicateLockTargetHash,
|
|
&target->tag,
|
|
targettaghash,
|
|
HASH_REMOVE, NULL);
|
|
Assert(rmtarget == target);
|
|
}
|
|
|
|
/*
|
|
* Delete child target locks owned by this process.
|
|
* This implementation is assuming that the usage of each target tag field
|
|
* is uniform. No need to make this hard if we don't have to.
|
|
*
|
|
* We acquire an LWLock in the case of parallel mode, because worker
|
|
* backends have access to the leader's SERIALIZABLEXACT. Otherwise,
|
|
* we aren't acquiring LWLocks for the predicate lock or lock
|
|
* target structures associated with this transaction unless we're going
|
|
* to modify them, because no other process is permitted to modify our
|
|
* locks.
|
|
*/
|
|
static void
|
|
DeleteChildTargetLocks(const PREDICATELOCKTARGETTAG *newtargettag)
|
|
{
|
|
SERIALIZABLEXACT *sxact;
|
|
PREDICATELOCK *predlock;
|
|
|
|
LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED);
|
|
sxact = MySerializableXact;
|
|
if (IsInParallelMode())
|
|
LWLockAcquire(&sxact->predicateLockListLock, LW_EXCLUSIVE);
|
|
predlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(sxact->predicateLocks),
|
|
&(sxact->predicateLocks),
|
|
offsetof(PREDICATELOCK, xactLink));
|
|
while (predlock)
|
|
{
|
|
SHM_QUEUE *predlocksxactlink;
|
|
PREDICATELOCK *nextpredlock;
|
|
PREDICATELOCKTAG oldlocktag;
|
|
PREDICATELOCKTARGET *oldtarget;
|
|
PREDICATELOCKTARGETTAG oldtargettag;
|
|
|
|
predlocksxactlink = &(predlock->xactLink);
|
|
nextpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(sxact->predicateLocks),
|
|
predlocksxactlink,
|
|
offsetof(PREDICATELOCK, xactLink));
|
|
|
|
oldlocktag = predlock->tag;
|
|
Assert(oldlocktag.myXact == sxact);
|
|
oldtarget = oldlocktag.myTarget;
|
|
oldtargettag = oldtarget->tag;
|
|
|
|
if (TargetTagIsCoveredBy(oldtargettag, *newtargettag))
|
|
{
|
|
uint32 oldtargettaghash;
|
|
LWLock *partitionLock;
|
|
PREDICATELOCK *rmpredlock PG_USED_FOR_ASSERTS_ONLY;
|
|
|
|
oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag);
|
|
partitionLock = PredicateLockHashPartitionLock(oldtargettaghash);
|
|
|
|
LWLockAcquire(partitionLock, LW_EXCLUSIVE);
|
|
|
|
SHMQueueDelete(predlocksxactlink);
|
|
SHMQueueDelete(&(predlock->targetLink));
|
|
rmpredlock = hash_search_with_hash_value
|
|
(PredicateLockHash,
|
|
&oldlocktag,
|
|
PredicateLockHashCodeFromTargetHashCode(&oldlocktag,
|
|
oldtargettaghash),
|
|
HASH_REMOVE, NULL);
|
|
Assert(rmpredlock == predlock);
|
|
|
|
RemoveTargetIfNoLongerUsed(oldtarget, oldtargettaghash);
|
|
|
|
LWLockRelease(partitionLock);
|
|
|
|
DecrementParentLocks(&oldtargettag);
|
|
}
|
|
|
|
predlock = nextpredlock;
|
|
}
|
|
if (IsInParallelMode())
|
|
LWLockRelease(&sxact->predicateLockListLock);
|
|
LWLockRelease(SerializablePredicateLockListLock);
|
|
}
|
|
|
|
/*
|
|
* Returns the promotion limit for a given predicate lock target. This is the
|
|
* max number of descendant locks allowed before promoting to the specified
|
|
* tag. Note that the limit includes non-direct descendants (e.g., both tuples
|
|
* and pages for a relation lock).
|
|
*
|
|
* Currently the default limit is 2 for a page lock, and half of the value of
|
|
* max_pred_locks_per_transaction - 1 for a relation lock, to match behavior
|
|
* of earlier releases when upgrading.
|
|
*
|
|
* TODO SSI: We should probably add additional GUCs to allow a maximum ratio
|
|
* of page and tuple locks based on the pages in a relation, and the maximum
|
|
* ratio of tuple locks to tuples in a page. This would provide more
|
|
* generally "balanced" allocation of locks to where they are most useful,
|
|
* while still allowing the absolute numbers to prevent one relation from
|
|
* tying up all predicate lock resources.
|
|
*/
|
|
static int
|
|
MaxPredicateChildLocks(const PREDICATELOCKTARGETTAG *tag)
|
|
{
|
|
switch (GET_PREDICATELOCKTARGETTAG_TYPE(*tag))
|
|
{
|
|
case PREDLOCKTAG_RELATION:
|
|
return max_predicate_locks_per_relation < 0
|
|
? (max_predicate_locks_per_xact
|
|
/ (-max_predicate_locks_per_relation)) - 1
|
|
: max_predicate_locks_per_relation;
|
|
|
|
case PREDLOCKTAG_PAGE:
|
|
return max_predicate_locks_per_page;
|
|
|
|
case PREDLOCKTAG_TUPLE:
|
|
|
|
/*
|
|
* not reachable: nothing is finer-granularity than a tuple, so we
|
|
* should never try to promote to it.
|
|
*/
|
|
Assert(false);
|
|
return 0;
|
|
}
|
|
|
|
/* not reachable */
|
|
Assert(false);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* For all ancestors of a newly-acquired predicate lock, increment
|
|
* their child count in the parent hash table. If any of them have
|
|
* more descendants than their promotion threshold, acquire the
|
|
* coarsest such lock.
|
|
*
|
|
* Returns true if a parent lock was acquired and false otherwise.
|
|
*/
|
|
static bool
|
|
CheckAndPromotePredicateLockRequest(const PREDICATELOCKTARGETTAG *reqtag)
|
|
{
|
|
PREDICATELOCKTARGETTAG targettag,
|
|
nexttag,
|
|
promotiontag;
|
|
LOCALPREDICATELOCK *parentlock;
|
|
bool found,
|
|
promote;
|
|
|
|
promote = false;
|
|
|
|
targettag = *reqtag;
|
|
|
|
/* check parents iteratively */
|
|
while (GetParentPredicateLockTag(&targettag, &nexttag))
|
|
{
|
|
targettag = nexttag;
|
|
parentlock = (LOCALPREDICATELOCK *) hash_search(LocalPredicateLockHash,
|
|
&targettag,
|
|
HASH_ENTER,
|
|
&found);
|
|
if (!found)
|
|
{
|
|
parentlock->held = false;
|
|
parentlock->childLocks = 1;
|
|
}
|
|
else
|
|
parentlock->childLocks++;
|
|
|
|
if (parentlock->childLocks >
|
|
MaxPredicateChildLocks(&targettag))
|
|
{
|
|
/*
|
|
* We should promote to this parent lock. Continue to check its
|
|
* ancestors, however, both to get their child counts right and to
|
|
* check whether we should just go ahead and promote to one of
|
|
* them.
|
|
*/
|
|
promotiontag = targettag;
|
|
promote = true;
|
|
}
|
|
}
|
|
|
|
if (promote)
|
|
{
|
|
/* acquire coarsest ancestor eligible for promotion */
|
|
PredicateLockAcquire(&promotiontag);
|
|
return true;
|
|
}
|
|
else
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* When releasing a lock, decrement the child count on all ancestor
|
|
* locks.
|
|
*
|
|
* This is called only when releasing a lock via
|
|
* DeleteChildTargetLocks (i.e. when a lock becomes redundant because
|
|
* we've acquired its parent, possibly due to promotion) or when a new
|
|
* MVCC write lock makes the predicate lock unnecessary. There's no
|
|
* point in calling it when locks are released at transaction end, as
|
|
* this information is no longer needed.
|
|
*/
|
|
static void
|
|
DecrementParentLocks(const PREDICATELOCKTARGETTAG *targettag)
|
|
{
|
|
PREDICATELOCKTARGETTAG parenttag,
|
|
nexttag;
|
|
|
|
parenttag = *targettag;
|
|
|
|
while (GetParentPredicateLockTag(&parenttag, &nexttag))
|
|
{
|
|
uint32 targettaghash;
|
|
LOCALPREDICATELOCK *parentlock,
|
|
*rmlock PG_USED_FOR_ASSERTS_ONLY;
|
|
|
|
parenttag = nexttag;
|
|
targettaghash = PredicateLockTargetTagHashCode(&parenttag);
|
|
parentlock = (LOCALPREDICATELOCK *)
|
|
hash_search_with_hash_value(LocalPredicateLockHash,
|
|
&parenttag, targettaghash,
|
|
HASH_FIND, NULL);
|
|
|
|
/*
|
|
* There's a small chance the parent lock doesn't exist in the lock
|
|
* table. This can happen if we prematurely removed it because an
|
|
* index split caused the child refcount to be off.
|
|
*/
|
|
if (parentlock == NULL)
|
|
continue;
|
|
|
|
parentlock->childLocks--;
|
|
|
|
/*
|
|
* Under similar circumstances the parent lock's refcount might be
|
|
* zero. This only happens if we're holding that lock (otherwise we
|
|
* would have removed the entry).
|
|
*/
|
|
if (parentlock->childLocks < 0)
|
|
{
|
|
Assert(parentlock->held);
|
|
parentlock->childLocks = 0;
|
|
}
|
|
|
|
if ((parentlock->childLocks == 0) && (!parentlock->held))
|
|
{
|
|
rmlock = (LOCALPREDICATELOCK *)
|
|
hash_search_with_hash_value(LocalPredicateLockHash,
|
|
&parenttag, targettaghash,
|
|
HASH_REMOVE, NULL);
|
|
Assert(rmlock == parentlock);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Indicate that a predicate lock on the given target is held by the
|
|
* specified transaction. Has no effect if the lock is already held.
|
|
*
|
|
* This updates the lock table and the sxact's lock list, and creates
|
|
* the lock target if necessary, but does *not* do anything related to
|
|
* granularity promotion or the local lock table. See
|
|
* PredicateLockAcquire for that.
|
|
*/
|
|
static void
|
|
CreatePredicateLock(const PREDICATELOCKTARGETTAG *targettag,
|
|
uint32 targettaghash,
|
|
SERIALIZABLEXACT *sxact)
|
|
{
|
|
PREDICATELOCKTARGET *target;
|
|
PREDICATELOCKTAG locktag;
|
|
PREDICATELOCK *lock;
|
|
LWLock *partitionLock;
|
|
bool found;
|
|
|
|
partitionLock = PredicateLockHashPartitionLock(targettaghash);
|
|
|
|
LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED);
|
|
if (IsInParallelMode())
|
|
LWLockAcquire(&sxact->predicateLockListLock, LW_EXCLUSIVE);
|
|
LWLockAcquire(partitionLock, LW_EXCLUSIVE);
|
|
|
|
/* Make sure that the target is represented. */
|
|
target = (PREDICATELOCKTARGET *)
|
|
hash_search_with_hash_value(PredicateLockTargetHash,
|
|
targettag, targettaghash,
|
|
HASH_ENTER_NULL, &found);
|
|
if (!target)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of shared memory"),
|
|
errhint("You might need to increase max_pred_locks_per_transaction.")));
|
|
if (!found)
|
|
SHMQueueInit(&(target->predicateLocks));
|
|
|
|
/* We've got the sxact and target, make sure they're joined. */
|
|
locktag.myTarget = target;
|
|
locktag.myXact = sxact;
|
|
lock = (PREDICATELOCK *)
|
|
hash_search_with_hash_value(PredicateLockHash, &locktag,
|
|
PredicateLockHashCodeFromTargetHashCode(&locktag, targettaghash),
|
|
HASH_ENTER_NULL, &found);
|
|
if (!lock)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of shared memory"),
|
|
errhint("You might need to increase max_pred_locks_per_transaction.")));
|
|
|
|
if (!found)
|
|
{
|
|
SHMQueueInsertBefore(&(target->predicateLocks), &(lock->targetLink));
|
|
SHMQueueInsertBefore(&(sxact->predicateLocks),
|
|
&(lock->xactLink));
|
|
lock->commitSeqNo = InvalidSerCommitSeqNo;
|
|
}
|
|
|
|
LWLockRelease(partitionLock);
|
|
if (IsInParallelMode())
|
|
LWLockRelease(&sxact->predicateLockListLock);
|
|
LWLockRelease(SerializablePredicateLockListLock);
|
|
}
|
|
|
|
/*
|
|
* Acquire a predicate lock on the specified target for the current
|
|
* connection if not already held. This updates the local lock table
|
|
* and uses it to implement granularity promotion. It will consolidate
|
|
* multiple locks into a coarser lock if warranted, and will release
|
|
* any finer-grained locks covered by the new one.
|
|
*/
|
|
static void
|
|
PredicateLockAcquire(const PREDICATELOCKTARGETTAG *targettag)
|
|
{
|
|
uint32 targettaghash;
|
|
bool found;
|
|
LOCALPREDICATELOCK *locallock;
|
|
|
|
/* Do we have the lock already, or a covering lock? */
|
|
if (PredicateLockExists(targettag))
|
|
return;
|
|
|
|
if (CoarserLockCovers(targettag))
|
|
return;
|
|
|
|
/* the same hash and LW lock apply to the lock target and the local lock. */
|
|
targettaghash = PredicateLockTargetTagHashCode(targettag);
|
|
|
|
/* Acquire lock in local table */
|
|
locallock = (LOCALPREDICATELOCK *)
|
|
hash_search_with_hash_value(LocalPredicateLockHash,
|
|
targettag, targettaghash,
|
|
HASH_ENTER, &found);
|
|
locallock->held = true;
|
|
if (!found)
|
|
locallock->childLocks = 0;
|
|
|
|
/* Actually create the lock */
|
|
CreatePredicateLock(targettag, targettaghash, MySerializableXact);
|
|
|
|
/*
|
|
* Lock has been acquired. Check whether it should be promoted to a
|
|
* coarser granularity, or whether there are finer-granularity locks to
|
|
* clean up.
|
|
*/
|
|
if (CheckAndPromotePredicateLockRequest(targettag))
|
|
{
|
|
/*
|
|
* Lock request was promoted to a coarser-granularity lock, and that
|
|
* lock was acquired. It will delete this lock and any of its
|
|
* children, so we're done.
|
|
*/
|
|
}
|
|
else
|
|
{
|
|
/* Clean up any finer-granularity locks */
|
|
if (GET_PREDICATELOCKTARGETTAG_TYPE(*targettag) != PREDLOCKTAG_TUPLE)
|
|
DeleteChildTargetLocks(targettag);
|
|
}
|
|
}
|
|
|
|
|
|
/*
|
|
* PredicateLockRelation
|
|
*
|
|
* Gets a predicate lock at the relation level.
|
|
* Skip if not in full serializable transaction isolation level.
|
|
* Skip if this is a temporary table.
|
|
* Clear any finer-grained predicate locks this session has on the relation.
|
|
*/
|
|
void
|
|
PredicateLockRelation(Relation relation, Snapshot snapshot)
|
|
{
|
|
PREDICATELOCKTARGETTAG tag;
|
|
|
|
if (!SerializationNeededForRead(relation, snapshot))
|
|
return;
|
|
|
|
SET_PREDICATELOCKTARGETTAG_RELATION(tag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id);
|
|
PredicateLockAcquire(&tag);
|
|
}
|
|
|
|
/*
|
|
* PredicateLockPage
|
|
*
|
|
* Gets a predicate lock at the page level.
|
|
* Skip if not in full serializable transaction isolation level.
|
|
* Skip if this is a temporary table.
|
|
* Skip if a coarser predicate lock already covers this page.
|
|
* Clear any finer-grained predicate locks this session has on the relation.
|
|
*/
|
|
void
|
|
PredicateLockPage(Relation relation, BlockNumber blkno, Snapshot snapshot)
|
|
{
|
|
PREDICATELOCKTARGETTAG tag;
|
|
|
|
if (!SerializationNeededForRead(relation, snapshot))
|
|
return;
|
|
|
|
SET_PREDICATELOCKTARGETTAG_PAGE(tag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id,
|
|
blkno);
|
|
PredicateLockAcquire(&tag);
|
|
}
|
|
|
|
/*
|
|
* PredicateLockTuple
|
|
*
|
|
* Gets a predicate lock at the tuple level.
|
|
* Skip if not in full serializable transaction isolation level.
|
|
* Skip if this is a temporary table.
|
|
*/
|
|
void
|
|
PredicateLockTuple(Relation relation, HeapTuple tuple, Snapshot snapshot)
|
|
{
|
|
PREDICATELOCKTARGETTAG tag;
|
|
ItemPointer tid;
|
|
TransactionId targetxmin;
|
|
|
|
if (!SerializationNeededForRead(relation, snapshot))
|
|
return;
|
|
|
|
/*
|
|
* If it's a heap tuple, return if this xact wrote it.
|
|
*/
|
|
if (relation->rd_index == NULL)
|
|
{
|
|
TransactionId myxid;
|
|
|
|
targetxmin = HeapTupleHeaderGetXmin(tuple->t_data);
|
|
|
|
myxid = GetTopTransactionIdIfAny();
|
|
if (TransactionIdIsValid(myxid))
|
|
{
|
|
if (TransactionIdFollowsOrEquals(targetxmin, TransactionXmin))
|
|
{
|
|
TransactionId xid = SubTransGetTopmostTransaction(targetxmin);
|
|
|
|
if (TransactionIdEquals(xid, myxid))
|
|
{
|
|
/* We wrote it; we already have a write lock. */
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Do quick-but-not-definitive test for a relation lock first. This will
|
|
* never cause a return when the relation is *not* locked, but will
|
|
* occasionally let the check continue when there really *is* a relation
|
|
* level lock.
|
|
*/
|
|
SET_PREDICATELOCKTARGETTAG_RELATION(tag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id);
|
|
if (PredicateLockExists(&tag))
|
|
return;
|
|
|
|
tid = &(tuple->t_self);
|
|
SET_PREDICATELOCKTARGETTAG_TUPLE(tag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id,
|
|
ItemPointerGetBlockNumber(tid),
|
|
ItemPointerGetOffsetNumber(tid));
|
|
PredicateLockAcquire(&tag);
|
|
}
|
|
|
|
|
|
/*
|
|
* DeleteLockTarget
|
|
*
|
|
* Remove a predicate lock target along with any locks held for it.
|
|
*
|
|
* Caller must hold SerializablePredicateLockListLock and the
|
|
* appropriate hash partition lock for the target.
|
|
*/
|
|
static void
|
|
DeleteLockTarget(PREDICATELOCKTARGET *target, uint32 targettaghash)
|
|
{
|
|
PREDICATELOCK *predlock;
|
|
SHM_QUEUE *predlocktargetlink;
|
|
PREDICATELOCK *nextpredlock;
|
|
bool found;
|
|
|
|
Assert(LWLockHeldByMeInMode(SerializablePredicateLockListLock,
|
|
LW_EXCLUSIVE));
|
|
Assert(LWLockHeldByMe(PredicateLockHashPartitionLock(targettaghash)));
|
|
|
|
predlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(target->predicateLocks),
|
|
&(target->predicateLocks),
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
while (predlock)
|
|
{
|
|
predlocktargetlink = &(predlock->targetLink);
|
|
nextpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(target->predicateLocks),
|
|
predlocktargetlink,
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
|
|
SHMQueueDelete(&(predlock->xactLink));
|
|
SHMQueueDelete(&(predlock->targetLink));
|
|
|
|
hash_search_with_hash_value
|
|
(PredicateLockHash,
|
|
&predlock->tag,
|
|
PredicateLockHashCodeFromTargetHashCode(&predlock->tag,
|
|
targettaghash),
|
|
HASH_REMOVE, &found);
|
|
Assert(found);
|
|
|
|
predlock = nextpredlock;
|
|
}
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
/* Remove the target itself, if possible. */
|
|
RemoveTargetIfNoLongerUsed(target, targettaghash);
|
|
}
|
|
|
|
|
|
/*
|
|
* TransferPredicateLocksToNewTarget
|
|
*
|
|
* Move or copy all the predicate locks for a lock target, for use by
|
|
* index page splits/combines and other things that create or replace
|
|
* lock targets. If 'removeOld' is true, the old locks and the target
|
|
* will be removed.
|
|
*
|
|
* Returns true on success, or false if we ran out of shared memory to
|
|
* allocate the new target or locks. Guaranteed to always succeed if
|
|
* removeOld is set (by using the scratch entry in PredicateLockTargetHash
|
|
* for scratch space).
|
|
*
|
|
* Warning: the "removeOld" option should be used only with care,
|
|
* because this function does not (indeed, can not) update other
|
|
* backends' LocalPredicateLockHash. If we are only adding new
|
|
* entries, this is not a problem: the local lock table is used only
|
|
* as a hint, so missing entries for locks that are held are
|
|
* OK. Having entries for locks that are no longer held, as can happen
|
|
* when using "removeOld", is not in general OK. We can only use it
|
|
* safely when replacing a lock with a coarser-granularity lock that
|
|
* covers it, or if we are absolutely certain that no one will need to
|
|
* refer to that lock in the future.
|
|
*
|
|
* Caller must hold SerializablePredicateLockListLock exclusively.
|
|
*/
|
|
static bool
|
|
TransferPredicateLocksToNewTarget(PREDICATELOCKTARGETTAG oldtargettag,
|
|
PREDICATELOCKTARGETTAG newtargettag,
|
|
bool removeOld)
|
|
{
|
|
uint32 oldtargettaghash;
|
|
LWLock *oldpartitionLock;
|
|
PREDICATELOCKTARGET *oldtarget;
|
|
uint32 newtargettaghash;
|
|
LWLock *newpartitionLock;
|
|
bool found;
|
|
bool outOfShmem = false;
|
|
|
|
Assert(LWLockHeldByMeInMode(SerializablePredicateLockListLock,
|
|
LW_EXCLUSIVE));
|
|
|
|
oldtargettaghash = PredicateLockTargetTagHashCode(&oldtargettag);
|
|
newtargettaghash = PredicateLockTargetTagHashCode(&newtargettag);
|
|
oldpartitionLock = PredicateLockHashPartitionLock(oldtargettaghash);
|
|
newpartitionLock = PredicateLockHashPartitionLock(newtargettaghash);
|
|
|
|
if (removeOld)
|
|
{
|
|
/*
|
|
* Remove the dummy entry to give us scratch space, so we know we'll
|
|
* be able to create the new lock target.
|
|
*/
|
|
RemoveScratchTarget(false);
|
|
}
|
|
|
|
/*
|
|
* We must get the partition locks in ascending sequence to avoid
|
|
* deadlocks. If old and new partitions are the same, we must request the
|
|
* lock only once.
|
|
*/
|
|
if (oldpartitionLock < newpartitionLock)
|
|
{
|
|
LWLockAcquire(oldpartitionLock,
|
|
(removeOld ? LW_EXCLUSIVE : LW_SHARED));
|
|
LWLockAcquire(newpartitionLock, LW_EXCLUSIVE);
|
|
}
|
|
else if (oldpartitionLock > newpartitionLock)
|
|
{
|
|
LWLockAcquire(newpartitionLock, LW_EXCLUSIVE);
|
|
LWLockAcquire(oldpartitionLock,
|
|
(removeOld ? LW_EXCLUSIVE : LW_SHARED));
|
|
}
|
|
else
|
|
LWLockAcquire(newpartitionLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Look for the old target. If not found, that's OK; no predicate locks
|
|
* are affected, so we can just clean up and return. If it does exist,
|
|
* walk its list of predicate locks and move or copy them to the new
|
|
* target.
|
|
*/
|
|
oldtarget = hash_search_with_hash_value(PredicateLockTargetHash,
|
|
&oldtargettag,
|
|
oldtargettaghash,
|
|
HASH_FIND, NULL);
|
|
|
|
if (oldtarget)
|
|
{
|
|
PREDICATELOCKTARGET *newtarget;
|
|
PREDICATELOCK *oldpredlock;
|
|
PREDICATELOCKTAG newpredlocktag;
|
|
|
|
newtarget = hash_search_with_hash_value(PredicateLockTargetHash,
|
|
&newtargettag,
|
|
newtargettaghash,
|
|
HASH_ENTER_NULL, &found);
|
|
|
|
if (!newtarget)
|
|
{
|
|
/* Failed to allocate due to insufficient shmem */
|
|
outOfShmem = true;
|
|
goto exit;
|
|
}
|
|
|
|
/* If we created a new entry, initialize it */
|
|
if (!found)
|
|
SHMQueueInit(&(newtarget->predicateLocks));
|
|
|
|
newpredlocktag.myTarget = newtarget;
|
|
|
|
/*
|
|
* Loop through all the locks on the old target, replacing them with
|
|
* locks on the new target.
|
|
*/
|
|
oldpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(oldtarget->predicateLocks),
|
|
&(oldtarget->predicateLocks),
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
while (oldpredlock)
|
|
{
|
|
SHM_QUEUE *predlocktargetlink;
|
|
PREDICATELOCK *nextpredlock;
|
|
PREDICATELOCK *newpredlock;
|
|
SerCommitSeqNo oldCommitSeqNo = oldpredlock->commitSeqNo;
|
|
|
|
predlocktargetlink = &(oldpredlock->targetLink);
|
|
nextpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(oldtarget->predicateLocks),
|
|
predlocktargetlink,
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
newpredlocktag.myXact = oldpredlock->tag.myXact;
|
|
|
|
if (removeOld)
|
|
{
|
|
SHMQueueDelete(&(oldpredlock->xactLink));
|
|
SHMQueueDelete(&(oldpredlock->targetLink));
|
|
|
|
hash_search_with_hash_value
|
|
(PredicateLockHash,
|
|
&oldpredlock->tag,
|
|
PredicateLockHashCodeFromTargetHashCode(&oldpredlock->tag,
|
|
oldtargettaghash),
|
|
HASH_REMOVE, &found);
|
|
Assert(found);
|
|
}
|
|
|
|
newpredlock = (PREDICATELOCK *)
|
|
hash_search_with_hash_value(PredicateLockHash,
|
|
&newpredlocktag,
|
|
PredicateLockHashCodeFromTargetHashCode(&newpredlocktag,
|
|
newtargettaghash),
|
|
HASH_ENTER_NULL,
|
|
&found);
|
|
if (!newpredlock)
|
|
{
|
|
/* Out of shared memory. Undo what we've done so far. */
|
|
LWLockRelease(SerializableXactHashLock);
|
|
DeleteLockTarget(newtarget, newtargettaghash);
|
|
outOfShmem = true;
|
|
goto exit;
|
|
}
|
|
if (!found)
|
|
{
|
|
SHMQueueInsertBefore(&(newtarget->predicateLocks),
|
|
&(newpredlock->targetLink));
|
|
SHMQueueInsertBefore(&(newpredlocktag.myXact->predicateLocks),
|
|
&(newpredlock->xactLink));
|
|
newpredlock->commitSeqNo = oldCommitSeqNo;
|
|
}
|
|
else
|
|
{
|
|
if (newpredlock->commitSeqNo < oldCommitSeqNo)
|
|
newpredlock->commitSeqNo = oldCommitSeqNo;
|
|
}
|
|
|
|
Assert(newpredlock->commitSeqNo != 0);
|
|
Assert((newpredlock->commitSeqNo == InvalidSerCommitSeqNo)
|
|
|| (newpredlock->tag.myXact == OldCommittedSxact));
|
|
|
|
oldpredlock = nextpredlock;
|
|
}
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
if (removeOld)
|
|
{
|
|
Assert(SHMQueueEmpty(&oldtarget->predicateLocks));
|
|
RemoveTargetIfNoLongerUsed(oldtarget, oldtargettaghash);
|
|
}
|
|
}
|
|
|
|
|
|
exit:
|
|
/* Release partition locks in reverse order of acquisition. */
|
|
if (oldpartitionLock < newpartitionLock)
|
|
{
|
|
LWLockRelease(newpartitionLock);
|
|
LWLockRelease(oldpartitionLock);
|
|
}
|
|
else if (oldpartitionLock > newpartitionLock)
|
|
{
|
|
LWLockRelease(oldpartitionLock);
|
|
LWLockRelease(newpartitionLock);
|
|
}
|
|
else
|
|
LWLockRelease(newpartitionLock);
|
|
|
|
if (removeOld)
|
|
{
|
|
/* We shouldn't run out of memory if we're moving locks */
|
|
Assert(!outOfShmem);
|
|
|
|
/* Put the scratch entry back */
|
|
RestoreScratchTarget(false);
|
|
}
|
|
|
|
return !outOfShmem;
|
|
}
|
|
|
|
/*
|
|
* Drop all predicate locks of any granularity from the specified relation,
|
|
* which can be a heap relation or an index relation. If 'transfer' is true,
|
|
* acquire a relation lock on the heap for any transactions with any lock(s)
|
|
* on the specified relation.
|
|
*
|
|
* This requires grabbing a lot of LW locks and scanning the entire lock
|
|
* target table for matches. That makes this more expensive than most
|
|
* predicate lock management functions, but it will only be called for DDL
|
|
* type commands that are expensive anyway, and there are fast returns when
|
|
* no serializable transactions are active or the relation is temporary.
|
|
*
|
|
* We don't use the TransferPredicateLocksToNewTarget function because it
|
|
* acquires its own locks on the partitions of the two targets involved,
|
|
* and we'll already be holding all partition locks.
|
|
*
|
|
* We can't throw an error from here, because the call could be from a
|
|
* transaction which is not serializable.
|
|
*
|
|
* NOTE: This is currently only called with transfer set to true, but that may
|
|
* change. If we decide to clean up the locks from a table on commit of a
|
|
* transaction which executed DROP TABLE, the false condition will be useful.
|
|
*/
|
|
static void
|
|
DropAllPredicateLocksFromTable(Relation relation, bool transfer)
|
|
{
|
|
HASH_SEQ_STATUS seqstat;
|
|
PREDICATELOCKTARGET *oldtarget;
|
|
PREDICATELOCKTARGET *heaptarget;
|
|
Oid dbId;
|
|
Oid relId;
|
|
Oid heapId;
|
|
int i;
|
|
bool isIndex;
|
|
bool found;
|
|
uint32 heaptargettaghash;
|
|
|
|
/*
|
|
* Bail out quickly if there are no serializable transactions running.
|
|
* It's safe to check this without taking locks because the caller is
|
|
* holding an ACCESS EXCLUSIVE lock on the relation. No new locks which
|
|
* would matter here can be acquired while that is held.
|
|
*/
|
|
if (!TransactionIdIsValid(PredXact->SxactGlobalXmin))
|
|
return;
|
|
|
|
if (!PredicateLockingNeededForRelation(relation))
|
|
return;
|
|
|
|
dbId = relation->rd_node.dbNode;
|
|
relId = relation->rd_id;
|
|
if (relation->rd_index == NULL)
|
|
{
|
|
isIndex = false;
|
|
heapId = relId;
|
|
}
|
|
else
|
|
{
|
|
isIndex = true;
|
|
heapId = relation->rd_index->indrelid;
|
|
}
|
|
Assert(heapId != InvalidOid);
|
|
Assert(transfer || !isIndex); /* index OID only makes sense with
|
|
* transfer */
|
|
|
|
/* Retrieve first time needed, then keep. */
|
|
heaptargettaghash = 0;
|
|
heaptarget = NULL;
|
|
|
|
/* Acquire locks on all lock partitions */
|
|
LWLockAcquire(SerializablePredicateLockListLock, LW_EXCLUSIVE);
|
|
for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++)
|
|
LWLockAcquire(PredicateLockHashPartitionLockByIndex(i), LW_EXCLUSIVE);
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Remove the dummy entry to give us scratch space, so we know we'll be
|
|
* able to create the new lock target.
|
|
*/
|
|
if (transfer)
|
|
RemoveScratchTarget(true);
|
|
|
|
/* Scan through target map */
|
|
hash_seq_init(&seqstat, PredicateLockTargetHash);
|
|
|
|
while ((oldtarget = (PREDICATELOCKTARGET *) hash_seq_search(&seqstat)))
|
|
{
|
|
PREDICATELOCK *oldpredlock;
|
|
|
|
/*
|
|
* Check whether this is a target which needs attention.
|
|
*/
|
|
if (GET_PREDICATELOCKTARGETTAG_RELATION(oldtarget->tag) != relId)
|
|
continue; /* wrong relation id */
|
|
if (GET_PREDICATELOCKTARGETTAG_DB(oldtarget->tag) != dbId)
|
|
continue; /* wrong database id */
|
|
if (transfer && !isIndex
|
|
&& GET_PREDICATELOCKTARGETTAG_TYPE(oldtarget->tag) == PREDLOCKTAG_RELATION)
|
|
continue; /* already the right lock */
|
|
|
|
/*
|
|
* If we made it here, we have work to do. We make sure the heap
|
|
* relation lock exists, then we walk the list of predicate locks for
|
|
* the old target we found, moving all locks to the heap relation lock
|
|
* -- unless they already hold that.
|
|
*/
|
|
|
|
/*
|
|
* First make sure we have the heap relation target. We only need to
|
|
* do this once.
|
|
*/
|
|
if (transfer && heaptarget == NULL)
|
|
{
|
|
PREDICATELOCKTARGETTAG heaptargettag;
|
|
|
|
SET_PREDICATELOCKTARGETTAG_RELATION(heaptargettag, dbId, heapId);
|
|
heaptargettaghash = PredicateLockTargetTagHashCode(&heaptargettag);
|
|
heaptarget = hash_search_with_hash_value(PredicateLockTargetHash,
|
|
&heaptargettag,
|
|
heaptargettaghash,
|
|
HASH_ENTER, &found);
|
|
if (!found)
|
|
SHMQueueInit(&heaptarget->predicateLocks);
|
|
}
|
|
|
|
/*
|
|
* Loop through all the locks on the old target, replacing them with
|
|
* locks on the new target.
|
|
*/
|
|
oldpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(oldtarget->predicateLocks),
|
|
&(oldtarget->predicateLocks),
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
while (oldpredlock)
|
|
{
|
|
PREDICATELOCK *nextpredlock;
|
|
PREDICATELOCK *newpredlock;
|
|
SerCommitSeqNo oldCommitSeqNo;
|
|
SERIALIZABLEXACT *oldXact;
|
|
|
|
nextpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(oldtarget->predicateLocks),
|
|
&(oldpredlock->targetLink),
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
|
|
/*
|
|
* Remove the old lock first. This avoids the chance of running
|
|
* out of lock structure entries for the hash table.
|
|
*/
|
|
oldCommitSeqNo = oldpredlock->commitSeqNo;
|
|
oldXact = oldpredlock->tag.myXact;
|
|
|
|
SHMQueueDelete(&(oldpredlock->xactLink));
|
|
|
|
/*
|
|
* No need for retail delete from oldtarget list, we're removing
|
|
* the whole target anyway.
|
|
*/
|
|
hash_search(PredicateLockHash,
|
|
&oldpredlock->tag,
|
|
HASH_REMOVE, &found);
|
|
Assert(found);
|
|
|
|
if (transfer)
|
|
{
|
|
PREDICATELOCKTAG newpredlocktag;
|
|
|
|
newpredlocktag.myTarget = heaptarget;
|
|
newpredlocktag.myXact = oldXact;
|
|
newpredlock = (PREDICATELOCK *)
|
|
hash_search_with_hash_value(PredicateLockHash,
|
|
&newpredlocktag,
|
|
PredicateLockHashCodeFromTargetHashCode(&newpredlocktag,
|
|
heaptargettaghash),
|
|
HASH_ENTER,
|
|
&found);
|
|
if (!found)
|
|
{
|
|
SHMQueueInsertBefore(&(heaptarget->predicateLocks),
|
|
&(newpredlock->targetLink));
|
|
SHMQueueInsertBefore(&(newpredlocktag.myXact->predicateLocks),
|
|
&(newpredlock->xactLink));
|
|
newpredlock->commitSeqNo = oldCommitSeqNo;
|
|
}
|
|
else
|
|
{
|
|
if (newpredlock->commitSeqNo < oldCommitSeqNo)
|
|
newpredlock->commitSeqNo = oldCommitSeqNo;
|
|
}
|
|
|
|
Assert(newpredlock->commitSeqNo != 0);
|
|
Assert((newpredlock->commitSeqNo == InvalidSerCommitSeqNo)
|
|
|| (newpredlock->tag.myXact == OldCommittedSxact));
|
|
}
|
|
|
|
oldpredlock = nextpredlock;
|
|
}
|
|
|
|
hash_search(PredicateLockTargetHash, &oldtarget->tag, HASH_REMOVE,
|
|
&found);
|
|
Assert(found);
|
|
}
|
|
|
|
/* Put the scratch entry back */
|
|
if (transfer)
|
|
RestoreScratchTarget(true);
|
|
|
|
/* Release locks in reverse order */
|
|
LWLockRelease(SerializableXactHashLock);
|
|
for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--)
|
|
LWLockRelease(PredicateLockHashPartitionLockByIndex(i));
|
|
LWLockRelease(SerializablePredicateLockListLock);
|
|
}
|
|
|
|
/*
|
|
* TransferPredicateLocksToHeapRelation
|
|
* For all transactions, transfer all predicate locks for the given
|
|
* relation to a single relation lock on the heap.
|
|
*/
|
|
void
|
|
TransferPredicateLocksToHeapRelation(Relation relation)
|
|
{
|
|
DropAllPredicateLocksFromTable(relation, true);
|
|
}
|
|
|
|
|
|
/*
|
|
* PredicateLockPageSplit
|
|
*
|
|
* Copies any predicate locks for the old page to the new page.
|
|
* Skip if this is a temporary table or toast table.
|
|
*
|
|
* NOTE: A page split (or overflow) affects all serializable transactions,
|
|
* even if it occurs in the context of another transaction isolation level.
|
|
*
|
|
* NOTE: This currently leaves the local copy of the locks without
|
|
* information on the new lock which is in shared memory. This could cause
|
|
* problems if enough page splits occur on locked pages without the processes
|
|
* which hold the locks getting in and noticing.
|
|
*/
|
|
void
|
|
PredicateLockPageSplit(Relation relation, BlockNumber oldblkno,
|
|
BlockNumber newblkno)
|
|
{
|
|
PREDICATELOCKTARGETTAG oldtargettag;
|
|
PREDICATELOCKTARGETTAG newtargettag;
|
|
bool success;
|
|
|
|
/*
|
|
* Bail out quickly if there are no serializable transactions running.
|
|
*
|
|
* It's safe to do this check without taking any additional locks. Even if
|
|
* a serializable transaction starts concurrently, we know it can't take
|
|
* any SIREAD locks on the page being split because the caller is holding
|
|
* the associated buffer page lock. Memory reordering isn't an issue; the
|
|
* memory barrier in the LWLock acquisition guarantees that this read
|
|
* occurs while the buffer page lock is held.
|
|
*/
|
|
if (!TransactionIdIsValid(PredXact->SxactGlobalXmin))
|
|
return;
|
|
|
|
if (!PredicateLockingNeededForRelation(relation))
|
|
return;
|
|
|
|
Assert(oldblkno != newblkno);
|
|
Assert(BlockNumberIsValid(oldblkno));
|
|
Assert(BlockNumberIsValid(newblkno));
|
|
|
|
SET_PREDICATELOCKTARGETTAG_PAGE(oldtargettag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id,
|
|
oldblkno);
|
|
SET_PREDICATELOCKTARGETTAG_PAGE(newtargettag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id,
|
|
newblkno);
|
|
|
|
LWLockAcquire(SerializablePredicateLockListLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Try copying the locks over to the new page's tag, creating it if
|
|
* necessary.
|
|
*/
|
|
success = TransferPredicateLocksToNewTarget(oldtargettag,
|
|
newtargettag,
|
|
false);
|
|
|
|
if (!success)
|
|
{
|
|
/*
|
|
* No more predicate lock entries are available. Failure isn't an
|
|
* option here, so promote the page lock to a relation lock.
|
|
*/
|
|
|
|
/* Get the parent relation lock's lock tag */
|
|
success = GetParentPredicateLockTag(&oldtargettag,
|
|
&newtargettag);
|
|
Assert(success);
|
|
|
|
/*
|
|
* Move the locks to the parent. This shouldn't fail.
|
|
*
|
|
* Note that here we are removing locks held by other backends,
|
|
* leading to a possible inconsistency in their local lock hash table.
|
|
* This is OK because we're replacing it with a lock that covers the
|
|
* old one.
|
|
*/
|
|
success = TransferPredicateLocksToNewTarget(oldtargettag,
|
|
newtargettag,
|
|
true);
|
|
Assert(success);
|
|
}
|
|
|
|
LWLockRelease(SerializablePredicateLockListLock);
|
|
}
|
|
|
|
/*
|
|
* PredicateLockPageCombine
|
|
*
|
|
* Combines predicate locks for two existing pages.
|
|
* Skip if this is a temporary table or toast table.
|
|
*
|
|
* NOTE: A page combine affects all serializable transactions, even if it
|
|
* occurs in the context of another transaction isolation level.
|
|
*/
|
|
void
|
|
PredicateLockPageCombine(Relation relation, BlockNumber oldblkno,
|
|
BlockNumber newblkno)
|
|
{
|
|
/*
|
|
* Page combines differ from page splits in that we ought to be able to
|
|
* remove the locks on the old page after transferring them to the new
|
|
* page, instead of duplicating them. However, because we can't edit other
|
|
* backends' local lock tables, removing the old lock would leave them
|
|
* with an entry in their LocalPredicateLockHash for a lock they're not
|
|
* holding, which isn't acceptable. So we wind up having to do the same
|
|
* work as a page split, acquiring a lock on the new page and keeping the
|
|
* old page locked too. That can lead to some false positives, but should
|
|
* be rare in practice.
|
|
*/
|
|
PredicateLockPageSplit(relation, oldblkno, newblkno);
|
|
}
|
|
|
|
/*
|
|
* Walk the list of in-progress serializable transactions and find the new
|
|
* xmin.
|
|
*/
|
|
static void
|
|
SetNewSxactGlobalXmin(void)
|
|
{
|
|
SERIALIZABLEXACT *sxact;
|
|
|
|
Assert(LWLockHeldByMe(SerializableXactHashLock));
|
|
|
|
PredXact->SxactGlobalXmin = InvalidTransactionId;
|
|
PredXact->SxactGlobalXminCount = 0;
|
|
|
|
for (sxact = FirstPredXact(); sxact != NULL; sxact = NextPredXact(sxact))
|
|
{
|
|
if (!SxactIsRolledBack(sxact)
|
|
&& !SxactIsCommitted(sxact)
|
|
&& sxact != OldCommittedSxact)
|
|
{
|
|
Assert(sxact->xmin != InvalidTransactionId);
|
|
if (!TransactionIdIsValid(PredXact->SxactGlobalXmin)
|
|
|| TransactionIdPrecedes(sxact->xmin,
|
|
PredXact->SxactGlobalXmin))
|
|
{
|
|
PredXact->SxactGlobalXmin = sxact->xmin;
|
|
PredXact->SxactGlobalXminCount = 1;
|
|
}
|
|
else if (TransactionIdEquals(sxact->xmin,
|
|
PredXact->SxactGlobalXmin))
|
|
PredXact->SxactGlobalXminCount++;
|
|
}
|
|
}
|
|
|
|
OldSerXidSetActiveSerXmin(PredXact->SxactGlobalXmin);
|
|
}
|
|
|
|
/*
|
|
* ReleasePredicateLocks
|
|
*
|
|
* Releases predicate locks based on completion of the current transaction,
|
|
* whether committed or rolled back. It can also be called for a read only
|
|
* transaction when it becomes impossible for the transaction to become
|
|
* part of a dangerous structure.
|
|
*
|
|
* We do nothing unless this is a serializable transaction.
|
|
*
|
|
* This method must ensure that shared memory hash tables are cleaned
|
|
* up in some relatively timely fashion.
|
|
*
|
|
* If this transaction is committing and is holding any predicate locks,
|
|
* it must be added to a list of completed serializable transactions still
|
|
* holding locks.
|
|
*
|
|
* If isReadOnlySafe is true, then predicate locks are being released before
|
|
* the end of the transaction because MySerializableXact has been determined
|
|
* to be RO_SAFE. In non-parallel mode we can release it completely, but it
|
|
* in parallel mode we partially release the SERIALIZABLEXACT and keep it
|
|
* around until the end of the transaction, allowing each backend to clear its
|
|
* MySerializableXact variable and benefit from the optimization in its own
|
|
* time.
|
|
*/
|
|
void
|
|
ReleasePredicateLocks(bool isCommit, bool isReadOnlySafe)
|
|
{
|
|
bool needToClear;
|
|
RWConflict conflict,
|
|
nextConflict,
|
|
possibleUnsafeConflict;
|
|
SERIALIZABLEXACT *roXact;
|
|
|
|
/*
|
|
* We can't trust XactReadOnly here, because a transaction which started
|
|
* as READ WRITE can show as READ ONLY later, e.g., within
|
|
* subtransactions. We want to flag a transaction as READ ONLY if it
|
|
* commits without writing so that de facto READ ONLY transactions get the
|
|
* benefit of some RO optimizations, so we will use this local variable to
|
|
* get some cleanup logic right which is based on whether the transaction
|
|
* was declared READ ONLY at the top level.
|
|
*/
|
|
bool topLevelIsDeclaredReadOnly;
|
|
|
|
/* We can't be both committing and releasing early due to RO_SAFE. */
|
|
Assert(!(isCommit && isReadOnlySafe));
|
|
|
|
/* Are we at the end of a transaction, that is, a commit or abort? */
|
|
if (!isReadOnlySafe)
|
|
{
|
|
/*
|
|
* Parallel workers mustn't release predicate locks at the end of
|
|
* their transaction. The leader will do that at the end of its
|
|
* transaction.
|
|
*/
|
|
if (IsParallelWorker())
|
|
{
|
|
ReleasePredicateLocksLocal();
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* By the time the leader in a parallel query reaches end of
|
|
* transaction, it has waited for all workers to exit.
|
|
*/
|
|
Assert(!ParallelContextActive());
|
|
|
|
/*
|
|
* If the leader in a parallel query earlier stashed a partially
|
|
* released SERIALIZABLEXACT for final clean-up at end of transaction
|
|
* (because workers might still have been accessing it), then it's
|
|
* time to restore it.
|
|
*/
|
|
if (SavedSerializableXact != InvalidSerializableXact)
|
|
{
|
|
Assert(MySerializableXact == InvalidSerializableXact);
|
|
MySerializableXact = SavedSerializableXact;
|
|
SavedSerializableXact = InvalidSerializableXact;
|
|
Assert(SxactIsPartiallyReleased(MySerializableXact));
|
|
}
|
|
}
|
|
|
|
if (MySerializableXact == InvalidSerializableXact)
|
|
{
|
|
Assert(LocalPredicateLockHash == NULL);
|
|
return;
|
|
}
|
|
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* If the transaction is committing, but it has been partially released
|
|
* already, then treat this as a roll back. It was marked as rolled back.
|
|
*/
|
|
if (isCommit && SxactIsPartiallyReleased(MySerializableXact))
|
|
isCommit = false;
|
|
|
|
/*
|
|
* If we're called in the middle of a transaction because we discovered
|
|
* that the SXACT_FLAG_RO_SAFE flag was set, then we'll partially release
|
|
* it (that is, release the predicate locks and conflicts, but not the
|
|
* SERIALIZABLEXACT itself) if we're the first backend to have noticed.
|
|
*/
|
|
if (isReadOnlySafe && IsInParallelMode())
|
|
{
|
|
/*
|
|
* The leader needs to stash a pointer to it, so that it can
|
|
* completely release it at end-of-transaction.
|
|
*/
|
|
if (!IsParallelWorker())
|
|
SavedSerializableXact = MySerializableXact;
|
|
|
|
/*
|
|
* The first backend to reach this condition will partially release
|
|
* the SERIALIZABLEXACT. All others will just clear their
|
|
* backend-local state so that they stop doing SSI checks for the rest
|
|
* of the transaction.
|
|
*/
|
|
if (SxactIsPartiallyReleased(MySerializableXact))
|
|
{
|
|
LWLockRelease(SerializableXactHashLock);
|
|
ReleasePredicateLocksLocal();
|
|
return;
|
|
}
|
|
else
|
|
{
|
|
MySerializableXact->flags |= SXACT_FLAG_PARTIALLY_RELEASED;
|
|
/* ... and proceed to perform the partial release below. */
|
|
}
|
|
}
|
|
Assert(!isCommit || SxactIsPrepared(MySerializableXact));
|
|
Assert(!isCommit || !SxactIsDoomed(MySerializableXact));
|
|
Assert(!SxactIsCommitted(MySerializableXact));
|
|
Assert(SxactIsPartiallyReleased(MySerializableXact)
|
|
|| !SxactIsRolledBack(MySerializableXact));
|
|
|
|
/* may not be serializable during COMMIT/ROLLBACK PREPARED */
|
|
Assert(MySerializableXact->pid == 0 || IsolationIsSerializable());
|
|
|
|
/* We'd better not already be on the cleanup list. */
|
|
Assert(!SxactIsOnFinishedList(MySerializableXact));
|
|
|
|
topLevelIsDeclaredReadOnly = SxactIsReadOnly(MySerializableXact);
|
|
|
|
/*
|
|
* We don't hold XidGenLock lock here, assuming that TransactionId is
|
|
* atomic!
|
|
*
|
|
* If this value is changing, we don't care that much whether we get the
|
|
* old or new value -- it is just used to determine how far
|
|
* SxactGlobalXmin must advance before this transaction can be fully
|
|
* cleaned up. The worst that could happen is we wait for one more
|
|
* transaction to complete before freeing some RAM; correctness of visible
|
|
* behavior is not affected.
|
|
*/
|
|
MySerializableXact->finishedBefore = XidFromFullTransactionId(ShmemVariableCache->nextFullXid);
|
|
|
|
/*
|
|
* If it's not a commit it's either a rollback or a read-only transaction
|
|
* flagged SXACT_FLAG_RO_SAFE, and we can clear our locks immediately.
|
|
*/
|
|
if (isCommit)
|
|
{
|
|
MySerializableXact->flags |= SXACT_FLAG_COMMITTED;
|
|
MySerializableXact->commitSeqNo = ++(PredXact->LastSxactCommitSeqNo);
|
|
/* Recognize implicit read-only transaction (commit without write). */
|
|
if (!MyXactDidWrite)
|
|
MySerializableXact->flags |= SXACT_FLAG_READ_ONLY;
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* The DOOMED flag indicates that we intend to roll back this
|
|
* transaction and so it should not cause serialization failures for
|
|
* other transactions that conflict with it. Note that this flag might
|
|
* already be set, if another backend marked this transaction for
|
|
* abort.
|
|
*
|
|
* The ROLLED_BACK flag further indicates that ReleasePredicateLocks
|
|
* has been called, and so the SerializableXact is eligible for
|
|
* cleanup. This means it should not be considered when calculating
|
|
* SxactGlobalXmin.
|
|
*/
|
|
MySerializableXact->flags |= SXACT_FLAG_DOOMED;
|
|
MySerializableXact->flags |= SXACT_FLAG_ROLLED_BACK;
|
|
|
|
/*
|
|
* If the transaction was previously prepared, but is now failing due
|
|
* to a ROLLBACK PREPARED or (hopefully very rare) error after the
|
|
* prepare, clear the prepared flag. This simplifies conflict
|
|
* checking.
|
|
*/
|
|
MySerializableXact->flags &= ~SXACT_FLAG_PREPARED;
|
|
}
|
|
|
|
if (!topLevelIsDeclaredReadOnly)
|
|
{
|
|
Assert(PredXact->WritableSxactCount > 0);
|
|
if (--(PredXact->WritableSxactCount) == 0)
|
|
{
|
|
/*
|
|
* Release predicate locks and rw-conflicts in for all committed
|
|
* transactions. There are no longer any transactions which might
|
|
* conflict with the locks and no chance for new transactions to
|
|
* overlap. Similarly, existing conflicts in can't cause pivots,
|
|
* and any conflicts in which could have completed a dangerous
|
|
* structure would already have caused a rollback, so any
|
|
* remaining ones must be benign.
|
|
*/
|
|
PredXact->CanPartialClearThrough = PredXact->LastSxactCommitSeqNo;
|
|
}
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Read-only transactions: clear the list of transactions that might
|
|
* make us unsafe. Note that we use 'inLink' for the iteration as
|
|
* opposed to 'outLink' for the r/w xacts.
|
|
*/
|
|
possibleUnsafeConflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->possibleUnsafeConflicts,
|
|
&MySerializableXact->possibleUnsafeConflicts,
|
|
offsetof(RWConflictData, inLink));
|
|
while (possibleUnsafeConflict)
|
|
{
|
|
nextConflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->possibleUnsafeConflicts,
|
|
&possibleUnsafeConflict->inLink,
|
|
offsetof(RWConflictData, inLink));
|
|
|
|
Assert(!SxactIsReadOnly(possibleUnsafeConflict->sxactOut));
|
|
Assert(MySerializableXact == possibleUnsafeConflict->sxactIn);
|
|
|
|
ReleaseRWConflict(possibleUnsafeConflict);
|
|
|
|
possibleUnsafeConflict = nextConflict;
|
|
}
|
|
}
|
|
|
|
/* Check for conflict out to old committed transactions. */
|
|
if (isCommit
|
|
&& !SxactIsReadOnly(MySerializableXact)
|
|
&& SxactHasSummaryConflictOut(MySerializableXact))
|
|
{
|
|
/*
|
|
* we don't know which old committed transaction we conflicted with,
|
|
* so be conservative and use FirstNormalSerCommitSeqNo here
|
|
*/
|
|
MySerializableXact->SeqNo.earliestOutConflictCommit =
|
|
FirstNormalSerCommitSeqNo;
|
|
MySerializableXact->flags |= SXACT_FLAG_CONFLICT_OUT;
|
|
}
|
|
|
|
/*
|
|
* Release all outConflicts to committed transactions. If we're rolling
|
|
* back clear them all. Set SXACT_FLAG_CONFLICT_OUT if any point to
|
|
* previously committed transactions.
|
|
*/
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->outConflicts,
|
|
&MySerializableXact->outConflicts,
|
|
offsetof(RWConflictData, outLink));
|
|
while (conflict)
|
|
{
|
|
nextConflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->outConflicts,
|
|
&conflict->outLink,
|
|
offsetof(RWConflictData, outLink));
|
|
|
|
if (isCommit
|
|
&& !SxactIsReadOnly(MySerializableXact)
|
|
&& SxactIsCommitted(conflict->sxactIn))
|
|
{
|
|
if ((MySerializableXact->flags & SXACT_FLAG_CONFLICT_OUT) == 0
|
|
|| conflict->sxactIn->prepareSeqNo < MySerializableXact->SeqNo.earliestOutConflictCommit)
|
|
MySerializableXact->SeqNo.earliestOutConflictCommit = conflict->sxactIn->prepareSeqNo;
|
|
MySerializableXact->flags |= SXACT_FLAG_CONFLICT_OUT;
|
|
}
|
|
|
|
if (!isCommit
|
|
|| SxactIsCommitted(conflict->sxactIn)
|
|
|| (conflict->sxactIn->SeqNo.lastCommitBeforeSnapshot >= PredXact->LastSxactCommitSeqNo))
|
|
ReleaseRWConflict(conflict);
|
|
|
|
conflict = nextConflict;
|
|
}
|
|
|
|
/*
|
|
* Release all inConflicts from committed and read-only transactions. If
|
|
* we're rolling back, clear them all.
|
|
*/
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->inConflicts,
|
|
&MySerializableXact->inConflicts,
|
|
offsetof(RWConflictData, inLink));
|
|
while (conflict)
|
|
{
|
|
nextConflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->inConflicts,
|
|
&conflict->inLink,
|
|
offsetof(RWConflictData, inLink));
|
|
|
|
if (!isCommit
|
|
|| SxactIsCommitted(conflict->sxactOut)
|
|
|| SxactIsReadOnly(conflict->sxactOut))
|
|
ReleaseRWConflict(conflict);
|
|
|
|
conflict = nextConflict;
|
|
}
|
|
|
|
if (!topLevelIsDeclaredReadOnly)
|
|
{
|
|
/*
|
|
* Remove ourselves from the list of possible conflicts for concurrent
|
|
* READ ONLY transactions, flagging them as unsafe if we have a
|
|
* conflict out. If any are waiting DEFERRABLE transactions, wake them
|
|
* up if they are known safe or known unsafe.
|
|
*/
|
|
possibleUnsafeConflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->possibleUnsafeConflicts,
|
|
&MySerializableXact->possibleUnsafeConflicts,
|
|
offsetof(RWConflictData, outLink));
|
|
while (possibleUnsafeConflict)
|
|
{
|
|
nextConflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->possibleUnsafeConflicts,
|
|
&possibleUnsafeConflict->outLink,
|
|
offsetof(RWConflictData, outLink));
|
|
|
|
roXact = possibleUnsafeConflict->sxactIn;
|
|
Assert(MySerializableXact == possibleUnsafeConflict->sxactOut);
|
|
Assert(SxactIsReadOnly(roXact));
|
|
|
|
/* Mark conflicted if necessary. */
|
|
if (isCommit
|
|
&& MyXactDidWrite
|
|
&& SxactHasConflictOut(MySerializableXact)
|
|
&& (MySerializableXact->SeqNo.earliestOutConflictCommit
|
|
<= roXact->SeqNo.lastCommitBeforeSnapshot))
|
|
{
|
|
/*
|
|
* This releases possibleUnsafeConflict (as well as all other
|
|
* possible conflicts for roXact)
|
|
*/
|
|
FlagSxactUnsafe(roXact);
|
|
}
|
|
else
|
|
{
|
|
ReleaseRWConflict(possibleUnsafeConflict);
|
|
|
|
/*
|
|
* If we were the last possible conflict, flag it safe. The
|
|
* transaction can now safely release its predicate locks (but
|
|
* that transaction's backend has to do that itself).
|
|
*/
|
|
if (SHMQueueEmpty(&roXact->possibleUnsafeConflicts))
|
|
roXact->flags |= SXACT_FLAG_RO_SAFE;
|
|
}
|
|
|
|
/*
|
|
* Wake up the process for a waiting DEFERRABLE transaction if we
|
|
* now know it's either safe or conflicted.
|
|
*/
|
|
if (SxactIsDeferrableWaiting(roXact) &&
|
|
(SxactIsROUnsafe(roXact) || SxactIsROSafe(roXact)))
|
|
ProcSendSignal(roXact->pid);
|
|
|
|
possibleUnsafeConflict = nextConflict;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Check whether it's time to clean up old transactions. This can only be
|
|
* done when the last serializable transaction with the oldest xmin among
|
|
* serializable transactions completes. We then find the "new oldest"
|
|
* xmin and purge any transactions which finished before this transaction
|
|
* was launched.
|
|
*/
|
|
needToClear = false;
|
|
if (TransactionIdEquals(MySerializableXact->xmin, PredXact->SxactGlobalXmin))
|
|
{
|
|
Assert(PredXact->SxactGlobalXminCount > 0);
|
|
if (--(PredXact->SxactGlobalXminCount) == 0)
|
|
{
|
|
SetNewSxactGlobalXmin();
|
|
needToClear = true;
|
|
}
|
|
}
|
|
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE);
|
|
|
|
/* Add this to the list of transactions to check for later cleanup. */
|
|
if (isCommit)
|
|
SHMQueueInsertBefore(FinishedSerializableTransactions,
|
|
&MySerializableXact->finishedLink);
|
|
|
|
/*
|
|
* If we're releasing a RO_SAFE transaction in parallel mode, we'll only
|
|
* partially release it. That's necessary because other backends may have
|
|
* a reference to it. The leader will release the SERIALIZABLEXACT itself
|
|
* at the end of the transaction after workers have stopped running.
|
|
*/
|
|
if (!isCommit)
|
|
ReleaseOneSerializableXact(MySerializableXact,
|
|
isReadOnlySafe && IsInParallelMode(),
|
|
false);
|
|
|
|
LWLockRelease(SerializableFinishedListLock);
|
|
|
|
if (needToClear)
|
|
ClearOldPredicateLocks();
|
|
|
|
ReleasePredicateLocksLocal();
|
|
}
|
|
|
|
static void
|
|
ReleasePredicateLocksLocal(void)
|
|
{
|
|
MySerializableXact = InvalidSerializableXact;
|
|
MyXactDidWrite = false;
|
|
|
|
/* Delete per-transaction lock table */
|
|
if (LocalPredicateLockHash != NULL)
|
|
{
|
|
hash_destroy(LocalPredicateLockHash);
|
|
LocalPredicateLockHash = NULL;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Clear old predicate locks, belonging to committed transactions that are no
|
|
* longer interesting to any in-progress transaction.
|
|
*/
|
|
static void
|
|
ClearOldPredicateLocks(void)
|
|
{
|
|
SERIALIZABLEXACT *finishedSxact;
|
|
PREDICATELOCK *predlock;
|
|
|
|
/*
|
|
* Loop through finished transactions. They are in commit order, so we can
|
|
* stop as soon as we find one that's still interesting.
|
|
*/
|
|
LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE);
|
|
finishedSxact = (SERIALIZABLEXACT *)
|
|
SHMQueueNext(FinishedSerializableTransactions,
|
|
FinishedSerializableTransactions,
|
|
offsetof(SERIALIZABLEXACT, finishedLink));
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
while (finishedSxact)
|
|
{
|
|
SERIALIZABLEXACT *nextSxact;
|
|
|
|
nextSxact = (SERIALIZABLEXACT *)
|
|
SHMQueueNext(FinishedSerializableTransactions,
|
|
&(finishedSxact->finishedLink),
|
|
offsetof(SERIALIZABLEXACT, finishedLink));
|
|
if (!TransactionIdIsValid(PredXact->SxactGlobalXmin)
|
|
|| TransactionIdPrecedesOrEquals(finishedSxact->finishedBefore,
|
|
PredXact->SxactGlobalXmin))
|
|
{
|
|
/*
|
|
* This transaction committed before any in-progress transaction
|
|
* took its snapshot. It's no longer interesting.
|
|
*/
|
|
LWLockRelease(SerializableXactHashLock);
|
|
SHMQueueDelete(&(finishedSxact->finishedLink));
|
|
ReleaseOneSerializableXact(finishedSxact, false, false);
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
}
|
|
else if (finishedSxact->commitSeqNo > PredXact->HavePartialClearedThrough
|
|
&& finishedSxact->commitSeqNo <= PredXact->CanPartialClearThrough)
|
|
{
|
|
/*
|
|
* Any active transactions that took their snapshot before this
|
|
* transaction committed are read-only, so we can clear part of
|
|
* its state.
|
|
*/
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
if (SxactIsReadOnly(finishedSxact))
|
|
{
|
|
/* A read-only transaction can be removed entirely */
|
|
SHMQueueDelete(&(finishedSxact->finishedLink));
|
|
ReleaseOneSerializableXact(finishedSxact, false, false);
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* A read-write transaction can only be partially cleared. We
|
|
* need to keep the SERIALIZABLEXACT but can release the
|
|
* SIREAD locks and conflicts in.
|
|
*/
|
|
ReleaseOneSerializableXact(finishedSxact, true, false);
|
|
}
|
|
|
|
PredXact->HavePartialClearedThrough = finishedSxact->commitSeqNo;
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
}
|
|
else
|
|
{
|
|
/* Still interesting. */
|
|
break;
|
|
}
|
|
finishedSxact = nextSxact;
|
|
}
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
/*
|
|
* Loop through predicate locks on dummy transaction for summarized data.
|
|
*/
|
|
LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED);
|
|
predlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&OldCommittedSxact->predicateLocks,
|
|
&OldCommittedSxact->predicateLocks,
|
|
offsetof(PREDICATELOCK, xactLink));
|
|
while (predlock)
|
|
{
|
|
PREDICATELOCK *nextpredlock;
|
|
bool canDoPartialCleanup;
|
|
|
|
nextpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&OldCommittedSxact->predicateLocks,
|
|
&predlock->xactLink,
|
|
offsetof(PREDICATELOCK, xactLink));
|
|
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
Assert(predlock->commitSeqNo != 0);
|
|
Assert(predlock->commitSeqNo != InvalidSerCommitSeqNo);
|
|
canDoPartialCleanup = (predlock->commitSeqNo <= PredXact->CanPartialClearThrough);
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
/*
|
|
* If this lock originally belonged to an old enough transaction, we
|
|
* can release it.
|
|
*/
|
|
if (canDoPartialCleanup)
|
|
{
|
|
PREDICATELOCKTAG tag;
|
|
PREDICATELOCKTARGET *target;
|
|
PREDICATELOCKTARGETTAG targettag;
|
|
uint32 targettaghash;
|
|
LWLock *partitionLock;
|
|
|
|
tag = predlock->tag;
|
|
target = tag.myTarget;
|
|
targettag = target->tag;
|
|
targettaghash = PredicateLockTargetTagHashCode(&targettag);
|
|
partitionLock = PredicateLockHashPartitionLock(targettaghash);
|
|
|
|
LWLockAcquire(partitionLock, LW_EXCLUSIVE);
|
|
|
|
SHMQueueDelete(&(predlock->targetLink));
|
|
SHMQueueDelete(&(predlock->xactLink));
|
|
|
|
hash_search_with_hash_value(PredicateLockHash, &tag,
|
|
PredicateLockHashCodeFromTargetHashCode(&tag,
|
|
targettaghash),
|
|
HASH_REMOVE, NULL);
|
|
RemoveTargetIfNoLongerUsed(target, targettaghash);
|
|
|
|
LWLockRelease(partitionLock);
|
|
}
|
|
|
|
predlock = nextpredlock;
|
|
}
|
|
|
|
LWLockRelease(SerializablePredicateLockListLock);
|
|
LWLockRelease(SerializableFinishedListLock);
|
|
}
|
|
|
|
/*
|
|
* This is the normal way to delete anything from any of the predicate
|
|
* locking hash tables. Given a transaction which we know can be deleted:
|
|
* delete all predicate locks held by that transaction and any predicate
|
|
* lock targets which are now unreferenced by a lock; delete all conflicts
|
|
* for the transaction; delete all xid values for the transaction; then
|
|
* delete the transaction.
|
|
*
|
|
* When the partial flag is set, we can release all predicate locks and
|
|
* in-conflict information -- we've established that there are no longer
|
|
* any overlapping read write transactions for which this transaction could
|
|
* matter -- but keep the transaction entry itself and any outConflicts.
|
|
*
|
|
* When the summarize flag is set, we've run short of room for sxact data
|
|
* and must summarize to the SLRU. Predicate locks are transferred to a
|
|
* dummy "old" transaction, with duplicate locks on a single target
|
|
* collapsing to a single lock with the "latest" commitSeqNo from among
|
|
* the conflicting locks..
|
|
*/
|
|
static void
|
|
ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
|
|
bool summarize)
|
|
{
|
|
PREDICATELOCK *predlock;
|
|
SERIALIZABLEXIDTAG sxidtag;
|
|
RWConflict conflict,
|
|
nextConflict;
|
|
|
|
Assert(sxact != NULL);
|
|
Assert(SxactIsRolledBack(sxact) || SxactIsCommitted(sxact));
|
|
Assert(partial || !SxactIsOnFinishedList(sxact));
|
|
Assert(LWLockHeldByMe(SerializableFinishedListLock));
|
|
|
|
/*
|
|
* First release all the predicate locks held by this xact (or transfer
|
|
* them to OldCommittedSxact if summarize is true)
|
|
*/
|
|
LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED);
|
|
if (IsInParallelMode())
|
|
LWLockAcquire(&sxact->predicateLockListLock, LW_EXCLUSIVE);
|
|
predlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(sxact->predicateLocks),
|
|
&(sxact->predicateLocks),
|
|
offsetof(PREDICATELOCK, xactLink));
|
|
while (predlock)
|
|
{
|
|
PREDICATELOCK *nextpredlock;
|
|
PREDICATELOCKTAG tag;
|
|
SHM_QUEUE *targetLink;
|
|
PREDICATELOCKTARGET *target;
|
|
PREDICATELOCKTARGETTAG targettag;
|
|
uint32 targettaghash;
|
|
LWLock *partitionLock;
|
|
|
|
nextpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(sxact->predicateLocks),
|
|
&(predlock->xactLink),
|
|
offsetof(PREDICATELOCK, xactLink));
|
|
|
|
tag = predlock->tag;
|
|
targetLink = &(predlock->targetLink);
|
|
target = tag.myTarget;
|
|
targettag = target->tag;
|
|
targettaghash = PredicateLockTargetTagHashCode(&targettag);
|
|
partitionLock = PredicateLockHashPartitionLock(targettaghash);
|
|
|
|
LWLockAcquire(partitionLock, LW_EXCLUSIVE);
|
|
|
|
SHMQueueDelete(targetLink);
|
|
|
|
hash_search_with_hash_value(PredicateLockHash, &tag,
|
|
PredicateLockHashCodeFromTargetHashCode(&tag,
|
|
targettaghash),
|
|
HASH_REMOVE, NULL);
|
|
if (summarize)
|
|
{
|
|
bool found;
|
|
|
|
/* Fold into dummy transaction list. */
|
|
tag.myXact = OldCommittedSxact;
|
|
predlock = hash_search_with_hash_value(PredicateLockHash, &tag,
|
|
PredicateLockHashCodeFromTargetHashCode(&tag,
|
|
targettaghash),
|
|
HASH_ENTER_NULL, &found);
|
|
if (!predlock)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of shared memory"),
|
|
errhint("You might need to increase max_pred_locks_per_transaction.")));
|
|
if (found)
|
|
{
|
|
Assert(predlock->commitSeqNo != 0);
|
|
Assert(predlock->commitSeqNo != InvalidSerCommitSeqNo);
|
|
if (predlock->commitSeqNo < sxact->commitSeqNo)
|
|
predlock->commitSeqNo = sxact->commitSeqNo;
|
|
}
|
|
else
|
|
{
|
|
SHMQueueInsertBefore(&(target->predicateLocks),
|
|
&(predlock->targetLink));
|
|
SHMQueueInsertBefore(&(OldCommittedSxact->predicateLocks),
|
|
&(predlock->xactLink));
|
|
predlock->commitSeqNo = sxact->commitSeqNo;
|
|
}
|
|
}
|
|
else
|
|
RemoveTargetIfNoLongerUsed(target, targettaghash);
|
|
|
|
LWLockRelease(partitionLock);
|
|
|
|
predlock = nextpredlock;
|
|
}
|
|
|
|
/*
|
|
* Rather than retail removal, just re-init the head after we've run
|
|
* through the list.
|
|
*/
|
|
SHMQueueInit(&sxact->predicateLocks);
|
|
|
|
if (IsInParallelMode())
|
|
LWLockRelease(&sxact->predicateLockListLock);
|
|
LWLockRelease(SerializablePredicateLockListLock);
|
|
|
|
sxidtag.xid = sxact->topXid;
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
|
|
/* Release all outConflicts (unless 'partial' is true) */
|
|
if (!partial)
|
|
{
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&sxact->outConflicts,
|
|
&sxact->outConflicts,
|
|
offsetof(RWConflictData, outLink));
|
|
while (conflict)
|
|
{
|
|
nextConflict = (RWConflict)
|
|
SHMQueueNext(&sxact->outConflicts,
|
|
&conflict->outLink,
|
|
offsetof(RWConflictData, outLink));
|
|
if (summarize)
|
|
conflict->sxactIn->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
|
|
ReleaseRWConflict(conflict);
|
|
conflict = nextConflict;
|
|
}
|
|
}
|
|
|
|
/* Release all inConflicts. */
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&sxact->inConflicts,
|
|
&sxact->inConflicts,
|
|
offsetof(RWConflictData, inLink));
|
|
while (conflict)
|
|
{
|
|
nextConflict = (RWConflict)
|
|
SHMQueueNext(&sxact->inConflicts,
|
|
&conflict->inLink,
|
|
offsetof(RWConflictData, inLink));
|
|
if (summarize)
|
|
conflict->sxactOut->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
|
|
ReleaseRWConflict(conflict);
|
|
conflict = nextConflict;
|
|
}
|
|
|
|
/* Finally, get rid of the xid and the record of the transaction itself. */
|
|
if (!partial)
|
|
{
|
|
if (sxidtag.xid != InvalidTransactionId)
|
|
hash_search(SerializableXidHash, &sxidtag, HASH_REMOVE, NULL);
|
|
ReleasePredXact(sxact);
|
|
}
|
|
|
|
LWLockRelease(SerializableXactHashLock);
|
|
}
|
|
|
|
/*
|
|
* Tests whether the given top level transaction is concurrent with
|
|
* (overlaps) our current transaction.
|
|
*
|
|
* We need to identify the top level transaction for SSI, anyway, so pass
|
|
* that to this function to save the overhead of checking the snapshot's
|
|
* subxip array.
|
|
*/
|
|
static bool
|
|
XidIsConcurrent(TransactionId xid)
|
|
{
|
|
Snapshot snap;
|
|
uint32 i;
|
|
|
|
Assert(TransactionIdIsValid(xid));
|
|
Assert(!TransactionIdEquals(xid, GetTopTransactionIdIfAny()));
|
|
|
|
snap = GetTransactionSnapshot();
|
|
|
|
if (TransactionIdPrecedes(xid, snap->xmin))
|
|
return false;
|
|
|
|
if (TransactionIdFollowsOrEquals(xid, snap->xmax))
|
|
return true;
|
|
|
|
for (i = 0; i < snap->xcnt; i++)
|
|
{
|
|
if (xid == snap->xip[i])
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* CheckForSerializableConflictOut
|
|
* We are reading a tuple which has been modified. If it is visible to
|
|
* us but has been deleted, that indicates a rw-conflict out. If it's
|
|
* not visible and was created by a concurrent (overlapping)
|
|
* serializable transaction, that is also a rw-conflict out,
|
|
*
|
|
* We will determine the top level xid of the writing transaction with which
|
|
* we may be in conflict, and check for overlap with our own transaction.
|
|
* If the transactions overlap (i.e., they cannot see each other's writes),
|
|
* then we have a conflict out.
|
|
*
|
|
* This function should be called just about anywhere in heapam.c where a
|
|
* tuple has been read. The caller must hold at least a shared lock on the
|
|
* buffer, because this function might set hint bits on the tuple. There is
|
|
* currently no known reason to call this function from an index AM.
|
|
*/
|
|
void
|
|
CheckForSerializableConflictOut(bool visible, Relation relation,
|
|
HeapTuple tuple, Buffer buffer,
|
|
Snapshot snapshot)
|
|
{
|
|
TransactionId xid;
|
|
SERIALIZABLEXIDTAG sxidtag;
|
|
SERIALIZABLEXID *sxid;
|
|
SERIALIZABLEXACT *sxact;
|
|
HTSV_Result htsvResult;
|
|
|
|
if (!SerializationNeededForRead(relation, snapshot))
|
|
return;
|
|
|
|
/* Check if someone else has already decided that we need to die */
|
|
if (SxactIsDoomed(MySerializableXact))
|
|
{
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("could not serialize access due to read/write dependencies among transactions"),
|
|
errdetail_internal("Reason code: Canceled on identification as a pivot, during conflict out checking."),
|
|
errhint("The transaction might succeed if retried.")));
|
|
}
|
|
|
|
/*
|
|
* Check to see whether the tuple has been written to by a concurrent
|
|
* transaction, either to create it not visible to us, or to delete it
|
|
* while it is visible to us. The "visible" bool indicates whether the
|
|
* tuple is visible to us, while HeapTupleSatisfiesVacuum checks what else
|
|
* is going on with it.
|
|
*/
|
|
htsvResult = HeapTupleSatisfiesVacuum(tuple, TransactionXmin, buffer);
|
|
switch (htsvResult)
|
|
{
|
|
case HEAPTUPLE_LIVE:
|
|
if (visible)
|
|
return;
|
|
xid = HeapTupleHeaderGetXmin(tuple->t_data);
|
|
break;
|
|
case HEAPTUPLE_RECENTLY_DEAD:
|
|
if (!visible)
|
|
return;
|
|
xid = HeapTupleHeaderGetUpdateXid(tuple->t_data);
|
|
break;
|
|
case HEAPTUPLE_DELETE_IN_PROGRESS:
|
|
xid = HeapTupleHeaderGetUpdateXid(tuple->t_data);
|
|
break;
|
|
case HEAPTUPLE_INSERT_IN_PROGRESS:
|
|
xid = HeapTupleHeaderGetXmin(tuple->t_data);
|
|
break;
|
|
case HEAPTUPLE_DEAD:
|
|
return;
|
|
default:
|
|
|
|
/*
|
|
* The only way to get to this default clause is if a new value is
|
|
* added to the enum type without adding it to this switch
|
|
* statement. That's a bug, so elog.
|
|
*/
|
|
elog(ERROR, "unrecognized return value from HeapTupleSatisfiesVacuum: %u", htsvResult);
|
|
|
|
/*
|
|
* In spite of having all enum values covered and calling elog on
|
|
* this default, some compilers think this is a code path which
|
|
* allows xid to be used below without initialization. Silence
|
|
* that warning.
|
|
*/
|
|
xid = InvalidTransactionId;
|
|
}
|
|
Assert(TransactionIdIsValid(xid));
|
|
Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
|
|
|
|
/*
|
|
* Find top level xid. Bail out if xid is too early to be a conflict, or
|
|
* if it's our own xid.
|
|
*/
|
|
if (TransactionIdEquals(xid, GetTopTransactionIdIfAny()))
|
|
return;
|
|
xid = SubTransGetTopmostTransaction(xid);
|
|
if (TransactionIdPrecedes(xid, TransactionXmin))
|
|
return;
|
|
if (TransactionIdEquals(xid, GetTopTransactionIdIfAny()))
|
|
return;
|
|
|
|
/*
|
|
* Find sxact or summarized info for the top level xid.
|
|
*/
|
|
sxidtag.xid = xid;
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
sxid = (SERIALIZABLEXID *)
|
|
hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL);
|
|
if (!sxid)
|
|
{
|
|
/*
|
|
* Transaction not found in "normal" SSI structures. Check whether it
|
|
* got pushed out to SLRU storage for "old committed" transactions.
|
|
*/
|
|
SerCommitSeqNo conflictCommitSeqNo;
|
|
|
|
conflictCommitSeqNo = OldSerXidGetMinConflictCommitSeqNo(xid);
|
|
if (conflictCommitSeqNo != 0)
|
|
{
|
|
if (conflictCommitSeqNo != InvalidSerCommitSeqNo
|
|
&& (!SxactIsReadOnly(MySerializableXact)
|
|
|| conflictCommitSeqNo
|
|
<= MySerializableXact->SeqNo.lastCommitBeforeSnapshot))
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("could not serialize access due to read/write dependencies among transactions"),
|
|
errdetail_internal("Reason code: Canceled on conflict out to old pivot %u.", xid),
|
|
errhint("The transaction might succeed if retried.")));
|
|
|
|
if (SxactHasSummaryConflictIn(MySerializableXact)
|
|
|| !SHMQueueEmpty(&MySerializableXact->inConflicts))
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("could not serialize access due to read/write dependencies among transactions"),
|
|
errdetail_internal("Reason code: Canceled on identification as a pivot, with conflict out to old committed transaction %u.", xid),
|
|
errhint("The transaction might succeed if retried.")));
|
|
|
|
MySerializableXact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
|
|
}
|
|
|
|
/* It's not serializable or otherwise not important. */
|
|
LWLockRelease(SerializableXactHashLock);
|
|
return;
|
|
}
|
|
sxact = sxid->myXact;
|
|
Assert(TransactionIdEquals(sxact->topXid, xid));
|
|
if (sxact == MySerializableXact || SxactIsDoomed(sxact))
|
|
{
|
|
/* Can't conflict with ourself or a transaction that will roll back. */
|
|
LWLockRelease(SerializableXactHashLock);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* We have a conflict out to a transaction which has a conflict out to a
|
|
* summarized transaction. That summarized transaction must have
|
|
* committed first, and we can't tell when it committed in relation to our
|
|
* snapshot acquisition, so something needs to be canceled.
|
|
*/
|
|
if (SxactHasSummaryConflictOut(sxact))
|
|
{
|
|
if (!SxactIsPrepared(sxact))
|
|
{
|
|
sxact->flags |= SXACT_FLAG_DOOMED;
|
|
LWLockRelease(SerializableXactHashLock);
|
|
return;
|
|
}
|
|
else
|
|
{
|
|
LWLockRelease(SerializableXactHashLock);
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("could not serialize access due to read/write dependencies among transactions"),
|
|
errdetail_internal("Reason code: Canceled on conflict out to old pivot."),
|
|
errhint("The transaction might succeed if retried.")));
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If this is a read-only transaction and the writing transaction has
|
|
* committed, and it doesn't have a rw-conflict to a transaction which
|
|
* committed before it, no conflict.
|
|
*/
|
|
if (SxactIsReadOnly(MySerializableXact)
|
|
&& SxactIsCommitted(sxact)
|
|
&& !SxactHasSummaryConflictOut(sxact)
|
|
&& (!SxactHasConflictOut(sxact)
|
|
|| MySerializableXact->SeqNo.lastCommitBeforeSnapshot < sxact->SeqNo.earliestOutConflictCommit))
|
|
{
|
|
/* Read-only transaction will appear to run first. No conflict. */
|
|
LWLockRelease(SerializableXactHashLock);
|
|
return;
|
|
}
|
|
|
|
if (!XidIsConcurrent(xid))
|
|
{
|
|
/* This write was already in our snapshot; no conflict. */
|
|
LWLockRelease(SerializableXactHashLock);
|
|
return;
|
|
}
|
|
|
|
if (RWConflictExists(MySerializableXact, sxact))
|
|
{
|
|
/* We don't want duplicate conflict records in the list. */
|
|
LWLockRelease(SerializableXactHashLock);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Flag the conflict. But first, if this conflict creates a dangerous
|
|
* structure, ereport an error.
|
|
*/
|
|
FlagRWConflict(MySerializableXact, sxact);
|
|
LWLockRelease(SerializableXactHashLock);
|
|
}
|
|
|
|
/*
|
|
* Check a particular target for rw-dependency conflict in. A subroutine of
|
|
* CheckForSerializableConflictIn().
|
|
*/
|
|
static void
|
|
CheckTargetForConflictsIn(PREDICATELOCKTARGETTAG *targettag)
|
|
{
|
|
uint32 targettaghash;
|
|
LWLock *partitionLock;
|
|
PREDICATELOCKTARGET *target;
|
|
PREDICATELOCK *predlock;
|
|
PREDICATELOCK *mypredlock = NULL;
|
|
PREDICATELOCKTAG mypredlocktag;
|
|
|
|
Assert(MySerializableXact != InvalidSerializableXact);
|
|
|
|
/*
|
|
* The same hash and LW lock apply to the lock target and the lock itself.
|
|
*/
|
|
targettaghash = PredicateLockTargetTagHashCode(targettag);
|
|
partitionLock = PredicateLockHashPartitionLock(targettaghash);
|
|
LWLockAcquire(partitionLock, LW_SHARED);
|
|
target = (PREDICATELOCKTARGET *)
|
|
hash_search_with_hash_value(PredicateLockTargetHash,
|
|
targettag, targettaghash,
|
|
HASH_FIND, NULL);
|
|
if (!target)
|
|
{
|
|
/* Nothing has this target locked; we're done here. */
|
|
LWLockRelease(partitionLock);
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Each lock for an overlapping transaction represents a conflict: a
|
|
* rw-dependency in to this transaction.
|
|
*/
|
|
predlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(target->predicateLocks),
|
|
&(target->predicateLocks),
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
while (predlock)
|
|
{
|
|
SHM_QUEUE *predlocktargetlink;
|
|
PREDICATELOCK *nextpredlock;
|
|
SERIALIZABLEXACT *sxact;
|
|
|
|
predlocktargetlink = &(predlock->targetLink);
|
|
nextpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(target->predicateLocks),
|
|
predlocktargetlink,
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
|
|
sxact = predlock->tag.myXact;
|
|
if (sxact == MySerializableXact)
|
|
{
|
|
/*
|
|
* If we're getting a write lock on a tuple, we don't need a
|
|
* predicate (SIREAD) lock on the same tuple. We can safely remove
|
|
* our SIREAD lock, but we'll defer doing so until after the loop
|
|
* because that requires upgrading to an exclusive partition lock.
|
|
*
|
|
* We can't use this optimization within a subtransaction because
|
|
* the subtransaction could roll back, and we would be left
|
|
* without any lock at the top level.
|
|
*/
|
|
if (!IsSubTransaction()
|
|
&& GET_PREDICATELOCKTARGETTAG_OFFSET(*targettag))
|
|
{
|
|
mypredlock = predlock;
|
|
mypredlocktag = predlock->tag;
|
|
}
|
|
}
|
|
else if (!SxactIsDoomed(sxact)
|
|
&& (!SxactIsCommitted(sxact)
|
|
|| TransactionIdPrecedes(GetTransactionSnapshot()->xmin,
|
|
sxact->finishedBefore))
|
|
&& !RWConflictExists(sxact, MySerializableXact))
|
|
{
|
|
LWLockRelease(SerializableXactHashLock);
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Re-check after getting exclusive lock because the other
|
|
* transaction may have flagged a conflict.
|
|
*/
|
|
if (!SxactIsDoomed(sxact)
|
|
&& (!SxactIsCommitted(sxact)
|
|
|| TransactionIdPrecedes(GetTransactionSnapshot()->xmin,
|
|
sxact->finishedBefore))
|
|
&& !RWConflictExists(sxact, MySerializableXact))
|
|
{
|
|
FlagRWConflict(sxact, MySerializableXact);
|
|
}
|
|
|
|
LWLockRelease(SerializableXactHashLock);
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
}
|
|
|
|
predlock = nextpredlock;
|
|
}
|
|
LWLockRelease(SerializableXactHashLock);
|
|
LWLockRelease(partitionLock);
|
|
|
|
/*
|
|
* If we found one of our own SIREAD locks to remove, remove it now.
|
|
*
|
|
* At this point our transaction already has a RowExclusiveLock on the
|
|
* relation, so we are OK to drop the predicate lock on the tuple, if
|
|
* found, without fearing that another write against the tuple will occur
|
|
* before the MVCC information makes it to the buffer.
|
|
*/
|
|
if (mypredlock != NULL)
|
|
{
|
|
uint32 predlockhashcode;
|
|
PREDICATELOCK *rmpredlock;
|
|
|
|
LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED);
|
|
if (IsInParallelMode())
|
|
LWLockAcquire(&MySerializableXact->predicateLockListLock, LW_EXCLUSIVE);
|
|
LWLockAcquire(partitionLock, LW_EXCLUSIVE);
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Remove the predicate lock from shared memory, if it wasn't removed
|
|
* while the locks were released. One way that could happen is from
|
|
* autovacuum cleaning up an index.
|
|
*/
|
|
predlockhashcode = PredicateLockHashCodeFromTargetHashCode
|
|
(&mypredlocktag, targettaghash);
|
|
rmpredlock = (PREDICATELOCK *)
|
|
hash_search_with_hash_value(PredicateLockHash,
|
|
&mypredlocktag,
|
|
predlockhashcode,
|
|
HASH_FIND, NULL);
|
|
if (rmpredlock != NULL)
|
|
{
|
|
Assert(rmpredlock == mypredlock);
|
|
|
|
SHMQueueDelete(&(mypredlock->targetLink));
|
|
SHMQueueDelete(&(mypredlock->xactLink));
|
|
|
|
rmpredlock = (PREDICATELOCK *)
|
|
hash_search_with_hash_value(PredicateLockHash,
|
|
&mypredlocktag,
|
|
predlockhashcode,
|
|
HASH_REMOVE, NULL);
|
|
Assert(rmpredlock == mypredlock);
|
|
|
|
RemoveTargetIfNoLongerUsed(target, targettaghash);
|
|
}
|
|
|
|
LWLockRelease(SerializableXactHashLock);
|
|
LWLockRelease(partitionLock);
|
|
if (IsInParallelMode())
|
|
LWLockRelease(&MySerializableXact->predicateLockListLock);
|
|
LWLockRelease(SerializablePredicateLockListLock);
|
|
|
|
if (rmpredlock != NULL)
|
|
{
|
|
/*
|
|
* Remove entry in local lock table if it exists. It's OK if it
|
|
* doesn't exist; that means the lock was transferred to a new
|
|
* target by a different backend.
|
|
*/
|
|
hash_search_with_hash_value(LocalPredicateLockHash,
|
|
targettag, targettaghash,
|
|
HASH_REMOVE, NULL);
|
|
|
|
DecrementParentLocks(targettag);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* CheckForSerializableConflictIn
|
|
* We are writing the given tuple. If that indicates a rw-conflict
|
|
* in from another serializable transaction, take appropriate action.
|
|
*
|
|
* Skip checking for any granularity for which a parameter is missing.
|
|
*
|
|
* A tuple update or delete is in conflict if we have a predicate lock
|
|
* against the relation or page in which the tuple exists, or against the
|
|
* tuple itself.
|
|
*/
|
|
void
|
|
CheckForSerializableConflictIn(Relation relation, HeapTuple tuple,
|
|
Buffer buffer)
|
|
{
|
|
PREDICATELOCKTARGETTAG targettag;
|
|
|
|
if (!SerializationNeededForWrite(relation))
|
|
return;
|
|
|
|
/* Check if someone else has already decided that we need to die */
|
|
if (SxactIsDoomed(MySerializableXact))
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("could not serialize access due to read/write dependencies among transactions"),
|
|
errdetail_internal("Reason code: Canceled on identification as a pivot, during conflict in checking."),
|
|
errhint("The transaction might succeed if retried.")));
|
|
|
|
/*
|
|
* We're doing a write which might cause rw-conflicts now or later.
|
|
* Memorize that fact.
|
|
*/
|
|
MyXactDidWrite = true;
|
|
|
|
/*
|
|
* It is important that we check for locks from the finest granularity to
|
|
* the coarsest granularity, so that granularity promotion doesn't cause
|
|
* us to miss a lock. The new (coarser) lock will be acquired before the
|
|
* old (finer) locks are released.
|
|
*
|
|
* It is not possible to take and hold a lock across the checks for all
|
|
* granularities because each target could be in a separate partition.
|
|
*/
|
|
if (tuple != NULL)
|
|
{
|
|
SET_PREDICATELOCKTARGETTAG_TUPLE(targettag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id,
|
|
ItemPointerGetBlockNumber(&(tuple->t_self)),
|
|
ItemPointerGetOffsetNumber(&(tuple->t_self)));
|
|
CheckTargetForConflictsIn(&targettag);
|
|
}
|
|
|
|
if (BufferIsValid(buffer))
|
|
{
|
|
SET_PREDICATELOCKTARGETTAG_PAGE(targettag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id,
|
|
BufferGetBlockNumber(buffer));
|
|
CheckTargetForConflictsIn(&targettag);
|
|
}
|
|
|
|
SET_PREDICATELOCKTARGETTAG_RELATION(targettag,
|
|
relation->rd_node.dbNode,
|
|
relation->rd_id);
|
|
CheckTargetForConflictsIn(&targettag);
|
|
}
|
|
|
|
/*
|
|
* CheckTableForSerializableConflictIn
|
|
* The entire table is going through a DDL-style logical mass delete
|
|
* like TRUNCATE or DROP TABLE. If that causes a rw-conflict in from
|
|
* another serializable transaction, take appropriate action.
|
|
*
|
|
* While these operations do not operate entirely within the bounds of
|
|
* snapshot isolation, they can occur inside a serializable transaction, and
|
|
* will logically occur after any reads which saw rows which were destroyed
|
|
* by these operations, so we do what we can to serialize properly under
|
|
* SSI.
|
|
*
|
|
* The relation passed in must be a heap relation. Any predicate lock of any
|
|
* granularity on the heap will cause a rw-conflict in to this transaction.
|
|
* Predicate locks on indexes do not matter because they only exist to guard
|
|
* against conflicting inserts into the index, and this is a mass *delete*.
|
|
* When a table is truncated or dropped, the index will also be truncated
|
|
* or dropped, and we'll deal with locks on the index when that happens.
|
|
*
|
|
* Dropping or truncating a table also needs to drop any existing predicate
|
|
* locks on heap tuples or pages, because they're about to go away. This
|
|
* should be done before altering the predicate locks because the transaction
|
|
* could be rolled back because of a conflict, in which case the lock changes
|
|
* are not needed. (At the moment, we don't actually bother to drop the
|
|
* existing locks on a dropped or truncated table at the moment. That might
|
|
* lead to some false positives, but it doesn't seem worth the trouble.)
|
|
*/
|
|
void
|
|
CheckTableForSerializableConflictIn(Relation relation)
|
|
{
|
|
HASH_SEQ_STATUS seqstat;
|
|
PREDICATELOCKTARGET *target;
|
|
Oid dbId;
|
|
Oid heapId;
|
|
int i;
|
|
|
|
/*
|
|
* Bail out quickly if there are no serializable transactions running.
|
|
* It's safe to check this without taking locks because the caller is
|
|
* holding an ACCESS EXCLUSIVE lock on the relation. No new locks which
|
|
* would matter here can be acquired while that is held.
|
|
*/
|
|
if (!TransactionIdIsValid(PredXact->SxactGlobalXmin))
|
|
return;
|
|
|
|
if (!SerializationNeededForWrite(relation))
|
|
return;
|
|
|
|
/*
|
|
* We're doing a write which might cause rw-conflicts now or later.
|
|
* Memorize that fact.
|
|
*/
|
|
MyXactDidWrite = true;
|
|
|
|
Assert(relation->rd_index == NULL); /* not an index relation */
|
|
|
|
dbId = relation->rd_node.dbNode;
|
|
heapId = relation->rd_id;
|
|
|
|
LWLockAcquire(SerializablePredicateLockListLock, LW_EXCLUSIVE);
|
|
for (i = 0; i < NUM_PREDICATELOCK_PARTITIONS; i++)
|
|
LWLockAcquire(PredicateLockHashPartitionLockByIndex(i), LW_SHARED);
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
|
|
/* Scan through target list */
|
|
hash_seq_init(&seqstat, PredicateLockTargetHash);
|
|
|
|
while ((target = (PREDICATELOCKTARGET *) hash_seq_search(&seqstat)))
|
|
{
|
|
PREDICATELOCK *predlock;
|
|
|
|
/*
|
|
* Check whether this is a target which needs attention.
|
|
*/
|
|
if (GET_PREDICATELOCKTARGETTAG_RELATION(target->tag) != heapId)
|
|
continue; /* wrong relation id */
|
|
if (GET_PREDICATELOCKTARGETTAG_DB(target->tag) != dbId)
|
|
continue; /* wrong database id */
|
|
|
|
/*
|
|
* Loop through locks for this target and flag conflicts.
|
|
*/
|
|
predlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(target->predicateLocks),
|
|
&(target->predicateLocks),
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
while (predlock)
|
|
{
|
|
PREDICATELOCK *nextpredlock;
|
|
|
|
nextpredlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(target->predicateLocks),
|
|
&(predlock->targetLink),
|
|
offsetof(PREDICATELOCK, targetLink));
|
|
|
|
if (predlock->tag.myXact != MySerializableXact
|
|
&& !RWConflictExists(predlock->tag.myXact, MySerializableXact))
|
|
{
|
|
FlagRWConflict(predlock->tag.myXact, MySerializableXact);
|
|
}
|
|
|
|
predlock = nextpredlock;
|
|
}
|
|
}
|
|
|
|
/* Release locks in reverse order */
|
|
LWLockRelease(SerializableXactHashLock);
|
|
for (i = NUM_PREDICATELOCK_PARTITIONS - 1; i >= 0; i--)
|
|
LWLockRelease(PredicateLockHashPartitionLockByIndex(i));
|
|
LWLockRelease(SerializablePredicateLockListLock);
|
|
}
|
|
|
|
|
|
/*
|
|
* Flag a rw-dependency between two serializable transactions.
|
|
*
|
|
* The caller is responsible for ensuring that we have a LW lock on
|
|
* the transaction hash table.
|
|
*/
|
|
static void
|
|
FlagRWConflict(SERIALIZABLEXACT *reader, SERIALIZABLEXACT *writer)
|
|
{
|
|
Assert(reader != writer);
|
|
|
|
/* First, see if this conflict causes failure. */
|
|
OnConflict_CheckForSerializationFailure(reader, writer);
|
|
|
|
/* Actually do the conflict flagging. */
|
|
if (reader == OldCommittedSxact)
|
|
writer->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
|
|
else if (writer == OldCommittedSxact)
|
|
reader->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
|
|
else
|
|
SetRWConflict(reader, writer);
|
|
}
|
|
|
|
/*----------------------------------------------------------------------------
|
|
* We are about to add a RW-edge to the dependency graph - check that we don't
|
|
* introduce a dangerous structure by doing so, and abort one of the
|
|
* transactions if so.
|
|
*
|
|
* A serialization failure can only occur if there is a dangerous structure
|
|
* in the dependency graph:
|
|
*
|
|
* Tin ------> Tpivot ------> Tout
|
|
* rw rw
|
|
*
|
|
* Furthermore, Tout must commit first.
|
|
*
|
|
* One more optimization is that if Tin is declared READ ONLY (or commits
|
|
* without writing), we can only have a problem if Tout committed before Tin
|
|
* acquired its snapshot.
|
|
*----------------------------------------------------------------------------
|
|
*/
|
|
static void
|
|
OnConflict_CheckForSerializationFailure(const SERIALIZABLEXACT *reader,
|
|
SERIALIZABLEXACT *writer)
|
|
{
|
|
bool failure;
|
|
RWConflict conflict;
|
|
|
|
Assert(LWLockHeldByMe(SerializableXactHashLock));
|
|
|
|
failure = false;
|
|
|
|
/*------------------------------------------------------------------------
|
|
* Check for already-committed writer with rw-conflict out flagged
|
|
* (conflict-flag on W means that T2 committed before W):
|
|
*
|
|
* R ------> W ------> T2
|
|
* rw rw
|
|
*
|
|
* That is a dangerous structure, so we must abort. (Since the writer
|
|
* has already committed, we must be the reader)
|
|
*------------------------------------------------------------------------
|
|
*/
|
|
if (SxactIsCommitted(writer)
|
|
&& (SxactHasConflictOut(writer) || SxactHasSummaryConflictOut(writer)))
|
|
failure = true;
|
|
|
|
/*------------------------------------------------------------------------
|
|
* Check whether the writer has become a pivot with an out-conflict
|
|
* committed transaction (T2), and T2 committed first:
|
|
*
|
|
* R ------> W ------> T2
|
|
* rw rw
|
|
*
|
|
* Because T2 must've committed first, there is no anomaly if:
|
|
* - the reader committed before T2
|
|
* - the writer committed before T2
|
|
* - the reader is a READ ONLY transaction and the reader was concurrent
|
|
* with T2 (= reader acquired its snapshot before T2 committed)
|
|
*
|
|
* We also handle the case that T2 is prepared but not yet committed
|
|
* here. In that case T2 has already checked for conflicts, so if it
|
|
* commits first, making the above conflict real, it's too late for it
|
|
* to abort.
|
|
*------------------------------------------------------------------------
|
|
*/
|
|
if (!failure)
|
|
{
|
|
if (SxactHasSummaryConflictOut(writer))
|
|
{
|
|
failure = true;
|
|
conflict = NULL;
|
|
}
|
|
else
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&writer->outConflicts,
|
|
&writer->outConflicts,
|
|
offsetof(RWConflictData, outLink));
|
|
while (conflict)
|
|
{
|
|
SERIALIZABLEXACT *t2 = conflict->sxactIn;
|
|
|
|
if (SxactIsPrepared(t2)
|
|
&& (!SxactIsCommitted(reader)
|
|
|| t2->prepareSeqNo <= reader->commitSeqNo)
|
|
&& (!SxactIsCommitted(writer)
|
|
|| t2->prepareSeqNo <= writer->commitSeqNo)
|
|
&& (!SxactIsReadOnly(reader)
|
|
|| t2->prepareSeqNo <= reader->SeqNo.lastCommitBeforeSnapshot))
|
|
{
|
|
failure = true;
|
|
break;
|
|
}
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&writer->outConflicts,
|
|
&conflict->outLink,
|
|
offsetof(RWConflictData, outLink));
|
|
}
|
|
}
|
|
|
|
/*------------------------------------------------------------------------
|
|
* Check whether the reader has become a pivot with a writer
|
|
* that's committed (or prepared):
|
|
*
|
|
* T0 ------> R ------> W
|
|
* rw rw
|
|
*
|
|
* Because W must've committed first for an anomaly to occur, there is no
|
|
* anomaly if:
|
|
* - T0 committed before the writer
|
|
* - T0 is READ ONLY, and overlaps the writer
|
|
*------------------------------------------------------------------------
|
|
*/
|
|
if (!failure && SxactIsPrepared(writer) && !SxactIsReadOnly(reader))
|
|
{
|
|
if (SxactHasSummaryConflictIn(reader))
|
|
{
|
|
failure = true;
|
|
conflict = NULL;
|
|
}
|
|
else
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&reader->inConflicts,
|
|
&reader->inConflicts,
|
|
offsetof(RWConflictData, inLink));
|
|
while (conflict)
|
|
{
|
|
SERIALIZABLEXACT *t0 = conflict->sxactOut;
|
|
|
|
if (!SxactIsDoomed(t0)
|
|
&& (!SxactIsCommitted(t0)
|
|
|| t0->commitSeqNo >= writer->prepareSeqNo)
|
|
&& (!SxactIsReadOnly(t0)
|
|
|| t0->SeqNo.lastCommitBeforeSnapshot >= writer->prepareSeqNo))
|
|
{
|
|
failure = true;
|
|
break;
|
|
}
|
|
conflict = (RWConflict)
|
|
SHMQueueNext(&reader->inConflicts,
|
|
&conflict->inLink,
|
|
offsetof(RWConflictData, inLink));
|
|
}
|
|
}
|
|
|
|
if (failure)
|
|
{
|
|
/*
|
|
* We have to kill a transaction to avoid a possible anomaly from
|
|
* occurring. If the writer is us, we can just ereport() to cause a
|
|
* transaction abort. Otherwise we flag the writer for termination,
|
|
* causing it to abort when it tries to commit. However, if the writer
|
|
* is a prepared transaction, already prepared, we can't abort it
|
|
* anymore, so we have to kill the reader instead.
|
|
*/
|
|
if (MySerializableXact == writer)
|
|
{
|
|
LWLockRelease(SerializableXactHashLock);
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("could not serialize access due to read/write dependencies among transactions"),
|
|
errdetail_internal("Reason code: Canceled on identification as a pivot, during write."),
|
|
errhint("The transaction might succeed if retried.")));
|
|
}
|
|
else if (SxactIsPrepared(writer))
|
|
{
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
/* if we're not the writer, we have to be the reader */
|
|
Assert(MySerializableXact == reader);
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("could not serialize access due to read/write dependencies among transactions"),
|
|
errdetail_internal("Reason code: Canceled on conflict out to pivot %u, during read.", writer->topXid),
|
|
errhint("The transaction might succeed if retried.")));
|
|
}
|
|
writer->flags |= SXACT_FLAG_DOOMED;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* PreCommit_CheckForSerializationFailure
|
|
* Check for dangerous structures in a serializable transaction
|
|
* at commit.
|
|
*
|
|
* We're checking for a dangerous structure as each conflict is recorded.
|
|
* The only way we could have a problem at commit is if this is the "out"
|
|
* side of a pivot, and neither the "in" side nor the pivot has yet
|
|
* committed.
|
|
*
|
|
* If a dangerous structure is found, the pivot (the near conflict) is
|
|
* marked for death, because rolling back another transaction might mean
|
|
* that we fail without ever making progress. This transaction is
|
|
* committing writes, so letting it commit ensures progress. If we
|
|
* canceled the far conflict, it might immediately fail again on retry.
|
|
*/
|
|
void
|
|
PreCommit_CheckForSerializationFailure(void)
|
|
{
|
|
RWConflict nearConflict;
|
|
|
|
if (MySerializableXact == InvalidSerializableXact)
|
|
return;
|
|
|
|
Assert(IsolationIsSerializable());
|
|
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
|
|
/* Check if someone else has already decided that we need to die */
|
|
if (SxactIsDoomed(MySerializableXact))
|
|
{
|
|
Assert(!SxactIsPartiallyReleased(MySerializableXact));
|
|
LWLockRelease(SerializableXactHashLock);
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("could not serialize access due to read/write dependencies among transactions"),
|
|
errdetail_internal("Reason code: Canceled on identification as a pivot, during commit attempt."),
|
|
errhint("The transaction might succeed if retried.")));
|
|
}
|
|
|
|
nearConflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->inConflicts,
|
|
&MySerializableXact->inConflicts,
|
|
offsetof(RWConflictData, inLink));
|
|
while (nearConflict)
|
|
{
|
|
if (!SxactIsCommitted(nearConflict->sxactOut)
|
|
&& !SxactIsDoomed(nearConflict->sxactOut))
|
|
{
|
|
RWConflict farConflict;
|
|
|
|
farConflict = (RWConflict)
|
|
SHMQueueNext(&nearConflict->sxactOut->inConflicts,
|
|
&nearConflict->sxactOut->inConflicts,
|
|
offsetof(RWConflictData, inLink));
|
|
while (farConflict)
|
|
{
|
|
if (farConflict->sxactOut == MySerializableXact
|
|
|| (!SxactIsCommitted(farConflict->sxactOut)
|
|
&& !SxactIsReadOnly(farConflict->sxactOut)
|
|
&& !SxactIsDoomed(farConflict->sxactOut)))
|
|
{
|
|
/*
|
|
* Normally, we kill the pivot transaction to make sure we
|
|
* make progress if the failing transaction is retried.
|
|
* However, we can't kill it if it's already prepared, so
|
|
* in that case we commit suicide instead.
|
|
*/
|
|
if (SxactIsPrepared(nearConflict->sxactOut))
|
|
{
|
|
LWLockRelease(SerializableXactHashLock);
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
|
|
errmsg("could not serialize access due to read/write dependencies among transactions"),
|
|
errdetail_internal("Reason code: Canceled on commit attempt with conflict in from prepared pivot."),
|
|
errhint("The transaction might succeed if retried.")));
|
|
}
|
|
nearConflict->sxactOut->flags |= SXACT_FLAG_DOOMED;
|
|
break;
|
|
}
|
|
farConflict = (RWConflict)
|
|
SHMQueueNext(&nearConflict->sxactOut->inConflicts,
|
|
&farConflict->inLink,
|
|
offsetof(RWConflictData, inLink));
|
|
}
|
|
}
|
|
|
|
nearConflict = (RWConflict)
|
|
SHMQueueNext(&MySerializableXact->inConflicts,
|
|
&nearConflict->inLink,
|
|
offsetof(RWConflictData, inLink));
|
|
}
|
|
|
|
MySerializableXact->prepareSeqNo = ++(PredXact->LastSxactCommitSeqNo);
|
|
MySerializableXact->flags |= SXACT_FLAG_PREPARED;
|
|
|
|
LWLockRelease(SerializableXactHashLock);
|
|
}
|
|
|
|
/*------------------------------------------------------------------------*/
|
|
|
|
/*
|
|
* Two-phase commit support
|
|
*/
|
|
|
|
/*
|
|
* AtPrepare_Locks
|
|
* Do the preparatory work for a PREPARE: make 2PC state file
|
|
* records for all predicate locks currently held.
|
|
*/
|
|
void
|
|
AtPrepare_PredicateLocks(void)
|
|
{
|
|
PREDICATELOCK *predlock;
|
|
SERIALIZABLEXACT *sxact;
|
|
TwoPhasePredicateRecord record;
|
|
TwoPhasePredicateXactRecord *xactRecord;
|
|
TwoPhasePredicateLockRecord *lockRecord;
|
|
|
|
sxact = MySerializableXact;
|
|
xactRecord = &(record.data.xactRecord);
|
|
lockRecord = &(record.data.lockRecord);
|
|
|
|
if (MySerializableXact == InvalidSerializableXact)
|
|
return;
|
|
|
|
/* Generate an xact record for our SERIALIZABLEXACT */
|
|
record.type = TWOPHASEPREDICATERECORD_XACT;
|
|
xactRecord->xmin = MySerializableXact->xmin;
|
|
xactRecord->flags = MySerializableXact->flags;
|
|
|
|
/*
|
|
* Note that we don't include the list of conflicts in our out in the
|
|
* statefile, because new conflicts can be added even after the
|
|
* transaction prepares. We'll just make a conservative assumption during
|
|
* recovery instead.
|
|
*/
|
|
|
|
RegisterTwoPhaseRecord(TWOPHASE_RM_PREDICATELOCK_ID, 0,
|
|
&record, sizeof(record));
|
|
|
|
/*
|
|
* Generate a lock record for each lock.
|
|
*
|
|
* To do this, we need to walk the predicate lock list in our sxact rather
|
|
* than using the local predicate lock table because the latter is not
|
|
* guaranteed to be accurate.
|
|
*/
|
|
LWLockAcquire(SerializablePredicateLockListLock, LW_SHARED);
|
|
|
|
/*
|
|
* No need to take sxact->predicateLockListLock in parallel mode because
|
|
* there cannot be any parallel workers running while we are preparing a
|
|
* transaction.
|
|
*/
|
|
Assert(!IsParallelWorker() && !ParallelContextActive());
|
|
|
|
predlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(sxact->predicateLocks),
|
|
&(sxact->predicateLocks),
|
|
offsetof(PREDICATELOCK, xactLink));
|
|
|
|
while (predlock != NULL)
|
|
{
|
|
record.type = TWOPHASEPREDICATERECORD_LOCK;
|
|
lockRecord->target = predlock->tag.myTarget->tag;
|
|
|
|
RegisterTwoPhaseRecord(TWOPHASE_RM_PREDICATELOCK_ID, 0,
|
|
&record, sizeof(record));
|
|
|
|
predlock = (PREDICATELOCK *)
|
|
SHMQueueNext(&(sxact->predicateLocks),
|
|
&(predlock->xactLink),
|
|
offsetof(PREDICATELOCK, xactLink));
|
|
}
|
|
|
|
LWLockRelease(SerializablePredicateLockListLock);
|
|
}
|
|
|
|
/*
|
|
* PostPrepare_Locks
|
|
* Clean up after successful PREPARE. Unlike the non-predicate
|
|
* lock manager, we do not need to transfer locks to a dummy
|
|
* PGPROC because our SERIALIZABLEXACT will stay around
|
|
* anyway. We only need to clean up our local state.
|
|
*/
|
|
void
|
|
PostPrepare_PredicateLocks(TransactionId xid)
|
|
{
|
|
if (MySerializableXact == InvalidSerializableXact)
|
|
return;
|
|
|
|
Assert(SxactIsPrepared(MySerializableXact));
|
|
|
|
MySerializableXact->pid = 0;
|
|
|
|
hash_destroy(LocalPredicateLockHash);
|
|
LocalPredicateLockHash = NULL;
|
|
|
|
MySerializableXact = InvalidSerializableXact;
|
|
MyXactDidWrite = false;
|
|
}
|
|
|
|
/*
|
|
* PredicateLockTwoPhaseFinish
|
|
* Release a prepared transaction's predicate locks once it
|
|
* commits or aborts.
|
|
*/
|
|
void
|
|
PredicateLockTwoPhaseFinish(TransactionId xid, bool isCommit)
|
|
{
|
|
SERIALIZABLEXID *sxid;
|
|
SERIALIZABLEXIDTAG sxidtag;
|
|
|
|
sxidtag.xid = xid;
|
|
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
sxid = (SERIALIZABLEXID *)
|
|
hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL);
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
/* xid will not be found if it wasn't a serializable transaction */
|
|
if (sxid == NULL)
|
|
return;
|
|
|
|
/* Release its locks */
|
|
MySerializableXact = sxid->myXact;
|
|
MyXactDidWrite = true; /* conservatively assume that we wrote
|
|
* something */
|
|
ReleasePredicateLocks(isCommit, false);
|
|
}
|
|
|
|
/*
|
|
* Re-acquire a predicate lock belonging to a transaction that was prepared.
|
|
*/
|
|
void
|
|
predicatelock_twophase_recover(TransactionId xid, uint16 info,
|
|
void *recdata, uint32 len)
|
|
{
|
|
TwoPhasePredicateRecord *record;
|
|
|
|
Assert(len == sizeof(TwoPhasePredicateRecord));
|
|
|
|
record = (TwoPhasePredicateRecord *) recdata;
|
|
|
|
Assert((record->type == TWOPHASEPREDICATERECORD_XACT) ||
|
|
(record->type == TWOPHASEPREDICATERECORD_LOCK));
|
|
|
|
if (record->type == TWOPHASEPREDICATERECORD_XACT)
|
|
{
|
|
/* Per-transaction record. Set up a SERIALIZABLEXACT. */
|
|
TwoPhasePredicateXactRecord *xactRecord;
|
|
SERIALIZABLEXACT *sxact;
|
|
SERIALIZABLEXID *sxid;
|
|
SERIALIZABLEXIDTAG sxidtag;
|
|
bool found;
|
|
|
|
xactRecord = (TwoPhasePredicateXactRecord *) &record->data.xactRecord;
|
|
|
|
LWLockAcquire(SerializableXactHashLock, LW_EXCLUSIVE);
|
|
sxact = CreatePredXact();
|
|
if (!sxact)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of shared memory")));
|
|
|
|
/* vxid for a prepared xact is InvalidBackendId/xid; no pid */
|
|
sxact->vxid.backendId = InvalidBackendId;
|
|
sxact->vxid.localTransactionId = (LocalTransactionId) xid;
|
|
sxact->pid = 0;
|
|
|
|
/* a prepared xact hasn't committed yet */
|
|
sxact->prepareSeqNo = RecoverySerCommitSeqNo;
|
|
sxact->commitSeqNo = InvalidSerCommitSeqNo;
|
|
sxact->finishedBefore = InvalidTransactionId;
|
|
|
|
sxact->SeqNo.lastCommitBeforeSnapshot = RecoverySerCommitSeqNo;
|
|
|
|
/*
|
|
* Don't need to track this; no transactions running at the time the
|
|
* recovered xact started are still active, except possibly other
|
|
* prepared xacts and we don't care whether those are RO_SAFE or not.
|
|
*/
|
|
SHMQueueInit(&(sxact->possibleUnsafeConflicts));
|
|
|
|
SHMQueueInit(&(sxact->predicateLocks));
|
|
SHMQueueElemInit(&(sxact->finishedLink));
|
|
|
|
sxact->topXid = xid;
|
|
sxact->xmin = xactRecord->xmin;
|
|
sxact->flags = xactRecord->flags;
|
|
Assert(SxactIsPrepared(sxact));
|
|
if (!SxactIsReadOnly(sxact))
|
|
{
|
|
++(PredXact->WritableSxactCount);
|
|
Assert(PredXact->WritableSxactCount <=
|
|
(MaxBackends + max_prepared_xacts));
|
|
}
|
|
|
|
/*
|
|
* We don't know whether the transaction had any conflicts or not, so
|
|
* we'll conservatively assume that it had both a conflict in and a
|
|
* conflict out, and represent that with the summary conflict flags.
|
|
*/
|
|
SHMQueueInit(&(sxact->outConflicts));
|
|
SHMQueueInit(&(sxact->inConflicts));
|
|
sxact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_IN;
|
|
sxact->flags |= SXACT_FLAG_SUMMARY_CONFLICT_OUT;
|
|
|
|
/* Register the transaction's xid */
|
|
sxidtag.xid = xid;
|
|
sxid = (SERIALIZABLEXID *) hash_search(SerializableXidHash,
|
|
&sxidtag,
|
|
HASH_ENTER, &found);
|
|
Assert(sxid != NULL);
|
|
Assert(!found);
|
|
sxid->myXact = (SERIALIZABLEXACT *) sxact;
|
|
|
|
/*
|
|
* Update global xmin. Note that this is a special case compared to
|
|
* registering a normal transaction, because the global xmin might go
|
|
* backwards. That's OK, because until recovery is over we're not
|
|
* going to complete any transactions or create any non-prepared
|
|
* transactions, so there's no danger of throwing away.
|
|
*/
|
|
if ((!TransactionIdIsValid(PredXact->SxactGlobalXmin)) ||
|
|
(TransactionIdFollows(PredXact->SxactGlobalXmin, sxact->xmin)))
|
|
{
|
|
PredXact->SxactGlobalXmin = sxact->xmin;
|
|
PredXact->SxactGlobalXminCount = 1;
|
|
OldSerXidSetActiveSerXmin(sxact->xmin);
|
|
}
|
|
else if (TransactionIdEquals(sxact->xmin, PredXact->SxactGlobalXmin))
|
|
{
|
|
Assert(PredXact->SxactGlobalXminCount > 0);
|
|
PredXact->SxactGlobalXminCount++;
|
|
}
|
|
|
|
LWLockRelease(SerializableXactHashLock);
|
|
}
|
|
else if (record->type == TWOPHASEPREDICATERECORD_LOCK)
|
|
{
|
|
/* Lock record. Recreate the PREDICATELOCK */
|
|
TwoPhasePredicateLockRecord *lockRecord;
|
|
SERIALIZABLEXID *sxid;
|
|
SERIALIZABLEXACT *sxact;
|
|
SERIALIZABLEXIDTAG sxidtag;
|
|
uint32 targettaghash;
|
|
|
|
lockRecord = (TwoPhasePredicateLockRecord *) &record->data.lockRecord;
|
|
targettaghash = PredicateLockTargetTagHashCode(&lockRecord->target);
|
|
|
|
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
|
|
sxidtag.xid = xid;
|
|
sxid = (SERIALIZABLEXID *)
|
|
hash_search(SerializableXidHash, &sxidtag, HASH_FIND, NULL);
|
|
LWLockRelease(SerializableXactHashLock);
|
|
|
|
Assert(sxid != NULL);
|
|
sxact = sxid->myXact;
|
|
Assert(sxact != InvalidSerializableXact);
|
|
|
|
CreatePredicateLock(&lockRecord->target, targettaghash, sxact);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Prepare to share the current SERIALIZABLEXACT with parallel workers.
|
|
* Return a handle object that can be used by AttachSerializableXact() in a
|
|
* parallel worker.
|
|
*/
|
|
SerializableXactHandle
|
|
ShareSerializableXact(void)
|
|
{
|
|
return MySerializableXact;
|
|
}
|
|
|
|
/*
|
|
* Allow parallel workers to import the leader's SERIALIZABLEXACT.
|
|
*/
|
|
void
|
|
AttachSerializableXact(SerializableXactHandle handle)
|
|
{
|
|
|
|
Assert(MySerializableXact == InvalidSerializableXact);
|
|
|
|
MySerializableXact = (SERIALIZABLEXACT *) handle;
|
|
if (MySerializableXact != InvalidSerializableXact)
|
|
CreateLocalPredicateLockHash();
|
|
}
|