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Revert "Avoid spurious deadlocks when upgrading a tuple lock" 

This reverts commits 3da73d6839 and de87a084c0.

This code has some tricky corner cases that I'm not sure are correct and
not properly tested anyway, so I'm reverting the whole thing for next
week's releases (reintroducing the deadlock bug that we set to fix).
I'll try again afterwards.

Discussion: https://postgr.es/m/E1hbXKQ-0003g1-0C@gemulon.postgresql.org
This commit is contained in:
Alvaro Herrera 2019-06-16 22:24:21 -04:00
parent 16c4e76f1b
commit 9d20b0ec8f
5 changed files with 21 additions and 280 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
src/backend/access/heap/README.tuplock
View File

@ -36,16 +36,6 @@ do LockTuple as well, if there is any conflict, to ensure that they don't
starve out waiting exclusive-lockers. However, if there is not any active
conflict for a tuple, we don't incur any extra overhead.
We make an exception to the above rule for those lockers that already hold
some lock on a tuple and attempt to acquire a stronger one on it. In that
case, we skip the LockTuple() call even when there are conflicts, provided
that the target tuple is being locked, updated or deleted by multiple sessions
concurrently. Failing to skip the lock would risk a deadlock, e.g., between a
session that was first to record its weaker lock in the tuple header and would
be waiting on the LockTuple() call to upgrade to the stronger lock level, and
another session that has already done LockTuple() and is waiting for the first
session transaction to release its tuple header-level lock.
We provide four levels of tuple locking strength: SELECT FOR UPDATE obtains an
exclusive lock which prevents any kind of modification of the tuple. This is
the lock level that is implicitly taken by DELETE operations, and also by

83
src/backend/access/heap/heapam.c
View File

@ -95,7 +95,7 @@ static void GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
static TransactionId MultiXactIdGetUpdateXid(TransactionId xmax,
uint16 t_infomask);
static bool DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
LockTupleMode lockmode, bool *current_is_member);
LockTupleMode lockmode);
static void MultiXactIdWait(MultiXactId multi, MultiXactStatus status, uint16 infomask,
Relation rel, ItemPointer ctid, XLTW_Oper oper,
int *remaining);
@ -2547,20 +2547,15 @@ l1:
*/
if (infomask & HEAP_XMAX_IS_MULTI)
{
bool current_is_member = false;
/* wait for multixact */
if (DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
LockTupleExclusive, &current_is_member))
LockTupleExclusive))
{
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
/*
* Acquire the lock, if necessary (but skip it when we're
* requesting a lock and already have one; avoids deadlock).
*/
if (!current_is_member)
heap_acquire_tuplock(relation, &(tp.t_self), LockTupleExclusive,
LockWaitBlock, &have_tuple_lock);
/* acquire tuple lock, if necessary */
heap_acquire_tuplock(relation, &(tp.t_self), LockTupleExclusive,
LockWaitBlock, &have_tuple_lock);
/* wait for multixact */
MultiXactIdWait((MultiXactId) xwait, MultiXactStatusUpdate, infomask,
@ -3131,20 +3126,15 @@ l2:
{
TransactionId update_xact;
int remain;
bool current_is_member = false;
if (DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
*lockmode, &current_is_member))
*lockmode))
{
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
/*
* Acquire the lock, if necessary (but skip it when we're
* requesting a lock and already have one; avoids deadlock).
*/
if (!current_is_member)
heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
LockWaitBlock, &have_tuple_lock);
/* acquire tuple lock, if necessary */
heap_acquire_tuplock(relation, &(oldtup.t_self), *lockmode,
LockWaitBlock, &have_tuple_lock);
/* wait for multixact */
MultiXactIdWait((MultiXactId) xwait, mxact_status, infomask,
@ -4038,7 +4028,6 @@ l3:
uint16 infomask;
uint16 infomask2;
bool require_sleep;
bool skip_tuple_lock = false;
ItemPointerData t_ctid;
/* must copy state data before unlocking buffer */
@ -4092,21 +4081,6 @@ l3:
result = TM_Ok;
goto out_unlocked;
}
else
{
/*
* Disable acquisition of the heavyweight tuple lock.
* Otherwise, when promoting a weaker lock, we might
* deadlock with another locker that has acquired the
* heavyweight tuple lock and is waiting for our
* transaction to finish.
*
* Note that in this case we still need to wait for
* the multixact if required, to avoid acquiring
* conflicting locks.
*/
skip_tuple_lock = true;
}
}
if (members)
@ -4261,7 +4235,7 @@ l3:
if (infomask & HEAP_XMAX_IS_MULTI)
{
if (!DoesMultiXactIdConflict((MultiXactId) xwait, infomask,
mode, NULL))
mode))
{
/*
* No conflict, but if the xmax changed under us in the
@ -4338,15 +4312,13 @@ l3:
/*
* Acquire tuple lock to establish our priority for the tuple, or
* die trying. LockTuple will release us when we are next-in-line
* for the tuple. We must do this even if we are share-locking,
* but not if we already have a weaker lock on the tuple.
* for the tuple. We must do this even if we are share-locking.
*
* If we are forced to "start over" below, we keep the tuple lock;
* this arranges that we stay at the head of the line while
* rechecking tuple state.
*/
if (!skip_tuple_lock &&
!heap_acquire_tuplock(relation, tid, mode, wait_policy,
if (!heap_acquire_tuplock(relation, tid, mode, wait_policy,
&have_tuple_lock))
{
/*
@ -6544,13 +6516,10 @@ HeapTupleGetUpdateXid(HeapTupleHeader tuple)
* tuple lock of the given strength?
*
* The passed infomask pairs up with the given multixact in the tuple header.
*
* If current_is_member is not NULL, it is set to 'true' if the current
* transaction is a member of the given multixact.
*/
static bool
DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
LockTupleMode lockmode, bool *current_is_member)
LockTupleMode lockmode)
{
int nmembers;
MultiXactMember *members;
@ -6571,26 +6540,17 @@ DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
TransactionId memxid;
LOCKMODE memlockmode;
if (result && (current_is_member == NULL || *current_is_member))
break;
memlockmode = LOCKMODE_from_mxstatus(members[i].status);
/* ignore members from current xact (but track their presence) */
memxid = members[i].xid;
if (TransactionIdIsCurrentTransactionId(memxid))
{
if (current_is_member != NULL)
*current_is_member = true;
continue;
}
else if (result)
continue;
/* ignore members that don't conflict with the lock we want */
if (!DoLockModesConflict(memlockmode, wanted))
continue;
/* ignore members from current xact */
memxid = members[i].xid;
if (TransactionIdIsCurrentTransactionId(memxid))
continue;
if (ISUPDATE_from_mxstatus(members[i].status))
{
/* ignore aborted updaters */
@ -6607,11 +6567,10 @@ DoesMultiXactIdConflict(MultiXactId multi, uint16 infomask,
/*
* Whatever remains are either live lockers that conflict with our
* wanted lock, and updaters that are not aborted. Those conflict
* with what we want. Set up to return true, but keep going to
* look for the current transaction among the multixact members,
* if needed.
* with what we want, so return true.
*/
result = true;
break;
}
pfree(members);
}

150
src/test/isolation/expected/tuplelock-upgrade-no-deadlock.out
View File

@ -1,150 +0,0 @@
Parsed test spec with 3 sessions
starting permutation: s1_share s2_for_update s3_share s3_for_update s1_rollback s3_rollback s2_rollback
step s1_share: select id from tlu_job where id = 1 for share;
id
1
step s2_for_update: select id from tlu_job where id = 1 for update; <waiting ...>
step s3_share: select id from tlu_job where id = 1 for share;
id
1
step s3_for_update: select id from tlu_job where id = 1 for update; <waiting ...>
step s1_rollback: rollback;
step s3_for_update: <... completed>
id
1
step s3_rollback: rollback;
step s2_for_update: <... completed>
id
1
step s2_rollback: rollback;
starting permutation: s1_keyshare s2_for_update s3_keyshare s1_update s3_update s1_rollback s3_rollback s2_rollback
step s1_keyshare: select id from tlu_job where id = 1 for key share;
id
1
step s2_for_update: select id from tlu_job where id = 1 for update; <waiting ...>
step s3_keyshare: select id from tlu_job where id = 1 for key share;
id
1
step s1_update: update tlu_job set name = 'b' where id = 1;
step s3_update: update tlu_job set name = 'c' where id = 1; <waiting ...>
step s1_rollback: rollback;
step s3_update: <... completed>
step s3_rollback: rollback;
step s2_for_update: <... completed>
id
1
step s2_rollback: rollback;
starting permutation: s1_keyshare s2_for_update s3_keyshare s1_update s3_update s1_commit s3_rollback s2_rollback
step s1_keyshare: select id from tlu_job where id = 1 for key share;
id
1
step s2_for_update: select id from tlu_job where id = 1 for update; <waiting ...>
step s3_keyshare: select id from tlu_job where id = 1 for key share;
id
1
step s1_update: update tlu_job set name = 'b' where id = 1;
step s3_update: update tlu_job set name = 'c' where id = 1; <waiting ...>
step s1_commit: commit;
step s3_update: <... completed>
step s3_rollback: rollback;
step s2_for_update: <... completed>
id
1
step s2_rollback: rollback;
starting permutation: s1_keyshare s2_for_update s3_keyshare s3_delete s1_rollback s3_rollback s2_rollback
step s1_keyshare: select id from tlu_job where id = 1 for key share;
id
1
step s2_for_update: select id from tlu_job where id = 1 for update; <waiting ...>
step s3_keyshare: select id from tlu_job where id = 1 for key share;
id
1
step s3_delete: delete from tlu_job where id = 1; <waiting ...>
step s1_rollback: rollback;
step s3_delete: <... completed>
step s3_rollback: rollback;
step s2_for_update: <... completed>
id
1
step s2_rollback: rollback;
starting permutation: s1_keyshare s2_for_update s3_keyshare s3_delete s1_rollback s3_commit s2_rollback
step s1_keyshare: select id from tlu_job where id = 1 for key share;
id
1
step s2_for_update: select id from tlu_job where id = 1 for update; <waiting ...>
step s3_keyshare: select id from tlu_job where id = 1 for key share;
id
1
step s3_delete: delete from tlu_job where id = 1; <waiting ...>
step s1_rollback: rollback;
step s3_delete: <... completed>
step s3_commit: commit;
step s2_for_update: <... completed>
id
step s2_rollback: rollback;
starting permutation: s1_share s2_for_update s3_for_update s1_rollback s2_rollback s3_rollback
step s1_share: select id from tlu_job where id = 1 for share;
id
1
step s2_for_update: select id from tlu_job where id = 1 for update; <waiting ...>
step s3_for_update: select id from tlu_job where id = 1 for update; <waiting ...>
step s1_rollback: rollback;
step s2_for_update: <... completed>
id
1
step s2_rollback: rollback;
step s3_for_update: <... completed>
id
1
step s3_rollback: rollback;
starting permutation: s1_share s2_update s3_update s1_rollback s2_rollback s3_rollback
step s1_share: select id from tlu_job where id = 1 for share;
id
1
step s2_update: update tlu_job set name = 'b' where id = 1; <waiting ...>
step s3_update: update tlu_job set name = 'c' where id = 1; <waiting ...>
step s1_rollback: rollback;
step s2_update: <... completed>
step s2_rollback: rollback;
step s3_update: <... completed>
step s3_rollback: rollback;
starting permutation: s1_share s2_delete s3_delete s1_rollback s2_rollback s3_rollback
step s1_share: select id from tlu_job where id = 1 for share;
id
1
step s2_delete: delete from tlu_job where id = 1; <waiting ...>
step s3_delete: delete from tlu_job where id = 1; <waiting ...>
step s1_rollback: rollback;
step s2_delete: <... completed>
step s2_rollback: rollback;
step s3_delete: <... completed>
step s3_rollback: rollback;

1
src/test/isolation/isolation_schedule
View File

@ -49,7 +49,6 @@ test: reindex-concurrently
test: propagate-lock-delete
test: tuplelock-conflict
test: tuplelock-update
test: tuplelock-upgrade-no-deadlock
test: freeze-the-dead
test: nowait
test: nowait-2

57
src/test/isolation/specs/tuplelock-upgrade-no-deadlock.spec
View File

@ -1,57 +0,0 @@
# This test checks that multiple sessions locking a single row in a table
# do not deadlock each other when one of them upgrades its existing lock
# while the others are waiting for it.
setup
{
drop table if exists tlu_job;
create table tlu_job (id integer primary key, name text);
insert into tlu_job values(1, 'a');
}
teardown
{
drop table tlu_job;
}
session "s1"
setup { begin; }
step "s1_keyshare" { select id from tlu_job where id = 1 for key share;}
step "s1_share" { select id from tlu_job where id = 1 for share; }
step "s1_update" { update tlu_job set name = 'b' where id = 1; }
step "s1_delete" { delete from tlu_job where id = 1; }
step "s1_rollback" { rollback; }
step "s1_commit" { commit; }
session "s2"
setup { begin; }
step "s2_for_update" { select id from tlu_job where id = 1 for update; }
step "s2_update" { update tlu_job set name = 'b' where id = 1; }
step "s2_delete" { delete from tlu_job where id = 1; }
step "s2_rollback" { rollback; }
step "s2_commit" { commit; }
session "s3"
setup { begin; }
step "s3_keyshare" { select id from tlu_job where id = 1 for key share; }
step "s3_share" { select id from tlu_job where id = 1 for share; }
step "s3_for_update" { select id from tlu_job where id = 1 for update; }
step "s3_update" { update tlu_job set name = 'c' where id = 1; }
step "s3_delete" { delete from tlu_job where id = 1; }
step "s3_rollback" { rollback; }
step "s3_commit" { commit; }
# test that s2 will not deadlock with s3 when s1 is rolled back
permutation "s1_share" "s2_for_update" "s3_share" "s3_for_update" "s1_rollback" "s3_rollback" "s2_rollback"
# test that update does not cause deadlocks if it can proceed
permutation "s1_keyshare" "s2_for_update" "s3_keyshare" "s1_update" "s3_update" "s1_rollback" "s3_rollback" "s2_rollback"
permutation "s1_keyshare" "s2_for_update" "s3_keyshare" "s1_update" "s3_update" "s1_commit" "s3_rollback" "s2_rollback"
# test that delete does not cause deadlocks if it can proceed
permutation "s1_keyshare" "s2_for_update" "s3_keyshare" "s3_delete" "s1_rollback" "s3_rollback" "s2_rollback"
permutation "s1_keyshare" "s2_for_update" "s3_keyshare" "s3_delete" "s1_rollback" "s3_commit" "s2_rollback"
# test that sessions that don't upgrade locks acquire them in order
permutation "s1_share" "s2_for_update" "s3_for_update" "s1_rollback" "s2_rollback" "s3_rollback"
permutation "s1_share" "s2_update" "s3_update" "s1_rollback" "s2_rollback" "s3_rollback"
permutation "s1_share" "s2_delete" "s3_delete" "s1_rollback" "s2_rollback" "s3_rollback"