457 lines
12 KiB
C
457 lines
12 KiB
C
/*-------------------------------------------------------------------------
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*
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* nodeLockRows.c
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* Routines to handle FOR UPDATE/FOR SHARE row locking
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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/executor/nodeLockRows.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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* ExecLockRows - fetch locked rows
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* ExecInitLockRows - initialize node and subnodes..
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* ExecEndLockRows - shutdown node and subnodes
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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/xact.h"
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#include "executor/executor.h"
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#include "executor/nodeLockRows.h"
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#include "foreign/fdwapi.h"
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#include "miscadmin.h"
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#include "storage/bufmgr.h"
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#include "utils/rel.h"
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/* ----------------------------------------------------------------
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* ExecLockRows
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* ----------------------------------------------------------------
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*/
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static TupleTableSlot * /* return: a tuple or NULL */
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ExecLockRows(PlanState *pstate)
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{
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LockRowsState *node = castNode(LockRowsState, pstate);
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TupleTableSlot *slot;
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EState *estate;
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PlanState *outerPlan;
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bool epq_needed;
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ListCell *lc;
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CHECK_FOR_INTERRUPTS();
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/*
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* get information from the node
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*/
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estate = node->ps.state;
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outerPlan = outerPlanState(node);
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/*
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* Get next tuple from subplan, if any.
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*/
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lnext:
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slot = ExecProcNode(outerPlan);
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if (TupIsNull(slot))
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return NULL;
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/* We don't need EvalPlanQual unless we get updated tuple version(s) */
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epq_needed = false;
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/*
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* Initialize EPQ machinery. Need to do that early because source tuples
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* are stored in slots initialized therein.
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*/
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EvalPlanQualBegin(&node->lr_epqstate, estate);
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/*
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* Attempt to lock the source tuple(s). (Note we only have locking
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* rowmarks in lr_arowMarks.)
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*/
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foreach(lc, node->lr_arowMarks)
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{
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ExecAuxRowMark *aerm = (ExecAuxRowMark *) lfirst(lc);
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ExecRowMark *erm = aerm->rowmark;
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Datum datum;
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bool isNull;
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HeapTupleData tuple;
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Buffer buffer;
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HeapUpdateFailureData hufd;
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LockTupleMode lockmode;
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HTSU_Result test;
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TupleTableSlot *markSlot;
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/* clear any leftover test tuple for this rel */
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markSlot = EvalPlanQualSlot(&node->lr_epqstate, erm->relation, erm->rti);
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ExecClearTuple(markSlot);
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/* if child rel, must check whether it produced this row */
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if (erm->rti != erm->prti)
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{
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Oid tableoid;
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datum = ExecGetJunkAttribute(slot,
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aerm->toidAttNo,
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&isNull);
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/* shouldn't ever get a null result... */
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if (isNull)
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elog(ERROR, "tableoid is NULL");
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tableoid = DatumGetObjectId(datum);
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Assert(OidIsValid(erm->relid));
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if (tableoid != erm->relid)
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{
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/* this child is inactive right now */
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erm->ermActive = false;
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ItemPointerSetInvalid(&(erm->curCtid));
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continue;
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}
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}
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erm->ermActive = true;
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/* fetch the tuple's ctid */
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datum = ExecGetJunkAttribute(slot,
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aerm->ctidAttNo,
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&isNull);
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/* shouldn't ever get a null result... */
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if (isNull)
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elog(ERROR, "ctid is NULL");
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/* requests for foreign tables must be passed to their FDW */
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if (erm->relation->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
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{
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FdwRoutine *fdwroutine;
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bool updated = false;
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fdwroutine = GetFdwRoutineForRelation(erm->relation, false);
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/* this should have been checked already, but let's be safe */
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if (fdwroutine->RefetchForeignRow == NULL)
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ereport(ERROR,
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(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
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errmsg("cannot lock rows in foreign table \"%s\"",
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RelationGetRelationName(erm->relation))));
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fdwroutine->RefetchForeignRow(estate,
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erm,
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datum,
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markSlot,
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&updated);
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if (TupIsNull(markSlot))
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{
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/* couldn't get the lock, so skip this row */
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goto lnext;
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}
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/*
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* if FDW says tuple was updated before getting locked, we need to
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* perform EPQ testing to see if quals are still satisfied
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*/
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if (updated)
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epq_needed = true;
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continue;
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}
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/* okay, try to lock the tuple */
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tuple.t_self = *((ItemPointer) DatumGetPointer(datum));
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switch (erm->markType)
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{
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case ROW_MARK_EXCLUSIVE:
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lockmode = LockTupleExclusive;
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break;
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case ROW_MARK_NOKEYEXCLUSIVE:
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lockmode = LockTupleNoKeyExclusive;
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break;
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case ROW_MARK_SHARE:
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lockmode = LockTupleShare;
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break;
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case ROW_MARK_KEYSHARE:
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lockmode = LockTupleKeyShare;
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break;
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default:
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elog(ERROR, "unsupported rowmark type");
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lockmode = LockTupleNoKeyExclusive; /* keep compiler quiet */
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break;
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}
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test = heap_lock_tuple(erm->relation, &tuple,
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estate->es_output_cid,
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lockmode, erm->waitPolicy, true,
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&buffer, &hufd);
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ReleaseBuffer(buffer);
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switch (test)
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{
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case HeapTupleWouldBlock:
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/* couldn't lock tuple in SKIP LOCKED mode */
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goto lnext;
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case HeapTupleSelfUpdated:
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/*
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* The target tuple was already updated or deleted by the
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* current command, or by a later command in the current
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* transaction. We *must* ignore the tuple in the former
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* case, so as to avoid the "Halloween problem" of repeated
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* update attempts. In the latter case it might be sensible
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* to fetch the updated tuple instead, but doing so would
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* require changing heap_update and heap_delete to not
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* complain about updating "invisible" tuples, which seems
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* pretty scary (heap_lock_tuple will not complain, but few
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* callers expect HeapTupleInvisible, and we're not one of
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* them). So for now, treat the tuple as deleted and do not
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* process.
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*/
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goto lnext;
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case HeapTupleMayBeUpdated:
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/* got the lock successfully */
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break;
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case HeapTupleUpdated:
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if (IsolationUsesXactSnapshot())
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ereport(ERROR,
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(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
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errmsg("could not serialize access due to concurrent update")));
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if (ItemPointerIndicatesMovedPartitions(&hufd.ctid))
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ereport(ERROR,
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(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
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errmsg("tuple to be locked was already moved to another partition due to concurrent update")));
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if (ItemPointerEquals(&hufd.ctid, &tuple.t_self))
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{
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/* Tuple was deleted, so don't return it */
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goto lnext;
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}
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/* updated, so fetch and lock the updated version */
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if (!EvalPlanQualFetch(estate, erm->relation,
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lockmode, erm->waitPolicy,
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&hufd.ctid, hufd.xmax,
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markSlot))
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{
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/*
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* Tuple was deleted; or it's locked and we're under SKIP
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* LOCKED policy, so don't return it
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*/
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goto lnext;
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}
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/* remember the actually locked tuple's TID */
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tuple.t_self = markSlot->tts_tid;
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/* Remember we need to do EPQ testing */
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epq_needed = true;
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/* Continue loop until we have all target tuples */
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break;
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case HeapTupleInvisible:
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elog(ERROR, "attempted to lock invisible tuple");
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break;
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default:
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elog(ERROR, "unrecognized heap_lock_tuple status: %u",
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test);
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}
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/* Remember locked tuple's TID for EPQ testing and WHERE CURRENT OF */
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erm->curCtid = tuple.t_self;
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}
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/*
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* If we need to do EvalPlanQual testing, do so.
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*/
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if (epq_needed)
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{
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/*
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* Fetch a copy of any rows that were successfully locked without any
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* update having occurred. (We do this in a separate pass so as to
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* avoid overhead in the common case where there are no concurrent
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* updates.) Make sure any inactive child rels have NULL test tuples
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* in EPQ.
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*/
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foreach(lc, node->lr_arowMarks)
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{
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ExecAuxRowMark *aerm = (ExecAuxRowMark *) lfirst(lc);
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ExecRowMark *erm = aerm->rowmark;
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TupleTableSlot *markSlot;
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HeapTupleData tuple;
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Buffer buffer;
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markSlot = EvalPlanQualSlot(&node->lr_epqstate, erm->relation, erm->rti);
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/* skip non-active child tables, but clear their test tuples */
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if (!erm->ermActive)
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{
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Assert(erm->rti != erm->prti); /* check it's child table */
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ExecClearTuple(markSlot);
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continue;
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}
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/* was tuple updated and fetched above? */
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if (!TupIsNull(markSlot))
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continue;
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/* foreign tables should have been fetched above */
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Assert(erm->relation->rd_rel->relkind != RELKIND_FOREIGN_TABLE);
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Assert(ItemPointerIsValid(&(erm->curCtid)));
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/* okay, fetch the tuple */
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tuple.t_self = erm->curCtid;
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if (!heap_fetch(erm->relation, SnapshotAny, &tuple, &buffer,
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false, NULL))
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elog(ERROR, "failed to fetch tuple for EvalPlanQual recheck");
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ExecStorePinnedBufferHeapTuple(&tuple, markSlot, buffer);
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ExecMaterializeSlot(markSlot);
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/* successful, use tuple in slot */
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}
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/*
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* Now fetch any non-locked source rows --- the EPQ logic knows how to
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* do that.
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*/
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EvalPlanQualSetSlot(&node->lr_epqstate, slot);
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EvalPlanQualFetchRowMarks(&node->lr_epqstate);
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/*
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* And finally we can re-evaluate the tuple.
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*/
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slot = EvalPlanQualNext(&node->lr_epqstate);
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if (TupIsNull(slot))
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{
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/* Updated tuple fails qual, so ignore it and go on */
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goto lnext;
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}
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}
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/* Got all locks, so return the current tuple */
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return slot;
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}
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/* ----------------------------------------------------------------
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* ExecInitLockRows
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*
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* This initializes the LockRows node state structures and
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* the node's subplan.
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* ----------------------------------------------------------------
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*/
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LockRowsState *
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ExecInitLockRows(LockRows *node, EState *estate, int eflags)
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{
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LockRowsState *lrstate;
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Plan *outerPlan = outerPlan(node);
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List *epq_arowmarks;
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ListCell *lc;
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/* check for unsupported flags */
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Assert(!(eflags & EXEC_FLAG_MARK));
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/*
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* create state structure
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*/
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lrstate = makeNode(LockRowsState);
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lrstate->ps.plan = (Plan *) node;
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lrstate->ps.state = estate;
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lrstate->ps.ExecProcNode = ExecLockRows;
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/*
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* Miscellaneous initialization
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*
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* LockRows nodes never call ExecQual or ExecProject, therefore no
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* ExprContext is needed.
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*/
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/*
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* Initialize result type.
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*/
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ExecInitResultTypeTL(&lrstate->ps);
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/*
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* then initialize outer plan
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*/
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outerPlanState(lrstate) = ExecInitNode(outerPlan, estate, eflags);
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/* node returns unmodified slots from the outer plan */
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lrstate->ps.resultopsset = true;
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lrstate->ps.resultops = ExecGetResultSlotOps(outerPlanState(lrstate),
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&lrstate->ps.resultopsfixed);
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/*
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* LockRows nodes do no projections, so initialize projection info for
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* this node appropriately
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*/
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lrstate->ps.ps_ProjInfo = NULL;
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/*
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* Locate the ExecRowMark(s) that this node is responsible for, and
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* construct ExecAuxRowMarks for them. (InitPlan should already have
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* built the global list of ExecRowMarks.)
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*/
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lrstate->lr_arowMarks = NIL;
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epq_arowmarks = NIL;
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foreach(lc, node->rowMarks)
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{
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PlanRowMark *rc = lfirst_node(PlanRowMark, lc);
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ExecRowMark *erm;
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ExecAuxRowMark *aerm;
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/* ignore "parent" rowmarks; they are irrelevant at runtime */
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if (rc->isParent)
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continue;
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/* find ExecRowMark and build ExecAuxRowMark */
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erm = ExecFindRowMark(estate, rc->rti, false);
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aerm = ExecBuildAuxRowMark(erm, outerPlan->targetlist);
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/*
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* Only locking rowmarks go into our own list. Non-locking marks are
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* passed off to the EvalPlanQual machinery. This is because we don't
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* want to bother fetching non-locked rows unless we actually have to
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* do an EPQ recheck.
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*/
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if (RowMarkRequiresRowShareLock(erm->markType))
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lrstate->lr_arowMarks = lappend(lrstate->lr_arowMarks, aerm);
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else
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epq_arowmarks = lappend(epq_arowmarks, aerm);
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}
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/* Now we have the info needed to set up EPQ state */
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EvalPlanQualInit(&lrstate->lr_epqstate, estate,
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outerPlan, epq_arowmarks, node->epqParam);
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return lrstate;
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}
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/* ----------------------------------------------------------------
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* ExecEndLockRows
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*
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* This shuts down the subplan and frees resources allocated
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* to this node.
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* ----------------------------------------------------------------
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*/
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void
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ExecEndLockRows(LockRowsState *node)
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{
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EvalPlanQualEnd(&node->lr_epqstate);
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ExecEndNode(outerPlanState(node));
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}
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void
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ExecReScanLockRows(LockRowsState *node)
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{
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/*
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* if chgParam of subnode is not null then plan will be re-scanned by
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* first ExecProcNode.
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*/
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if (node->ps.lefttree->chgParam == NULL)
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ExecReScan(node->ps.lefttree);
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}
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