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nodeLockRows.c
nodeLockRows.c 12.33 KiB
/*-------------------------------------------------------------------------
*
* nodeLockRows.c
* Routines to handle FOR UPDATE/FOR SHARE row locking
*
* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/executor/nodeLockRows.c
*
*-------------------------------------------------------------------------
*/
/*
* INTERFACE ROUTINES
* ExecLockRows - fetch locked rows
* ExecInitLockRows - initialize node and subnodes..
* ExecEndLockRows - shutdown node and subnodes
*/
#include "postgres.h"
#include "access/htup_details.h"
#include "access/xact.h"
#include "executor/executor.h"
#include "executor/nodeLockRows.h"
#include "foreign/fdwapi.h"
#include "storage/bufmgr.h"
#include "utils/rel.h"
#include "utils/tqual.h"
/* ----------------------------------------------------------------
* ExecLockRows
* ----------------------------------------------------------------
*/
TupleTableSlot * /* return: a tuple or NULL */
ExecLockRows(LockRowsState *node)
{
TupleTableSlot *slot;
EState *estate;
PlanState *outerPlan;
bool epq_needed;
ListCell *lc;
/*
* get information from the node
*/
estate = node->ps.state;
outerPlan = outerPlanState(node);
/*
* Get next tuple from subplan, if any.
*/
lnext:
slot = ExecProcNode(outerPlan);
if (TupIsNull(slot))
return NULL;
/* We don't need EvalPlanQual unless we get updated tuple version(s) */
epq_needed = false;
/*
* Attempt to lock the source tuple(s). (Note we only have locking
* rowmarks in lr_arowMarks.)
*/
foreach(lc, node->lr_arowMarks)
{ ExecAuxRowMark *aerm = (ExecAuxRowMark *) lfirst(lc);
ExecRowMark *erm = aerm->rowmark;
HeapTuple *testTuple;
Datum datum;
bool isNull;
HeapTupleData tuple;
Buffer buffer;
HeapUpdateFailureData hufd;
LockTupleMode lockmode;
HTSU_Result test;
HeapTuple copyTuple;
/* clear any leftover test tuple for this rel */
testTuple = &(node->lr_curtuples[erm->rti - 1]);
if (*testTuple != NULL)
heap_freetuple(*testTuple);
*testTuple = NULL;
/* if child rel, must check whether it produced this row */
if (erm->rti != erm->prti)
{
Oid tableoid;
datum = ExecGetJunkAttribute(slot,
aerm->toidAttNo,
&isNull);
/* shouldn't ever get a null result... */
if (isNull)
elog(ERROR, "tableoid is NULL");
tableoid = DatumGetObjectId(datum);
Assert(OidIsValid(erm->relid));
if (tableoid != erm->relid)
{
/* this child is inactive right now */
erm->ermActive = false;
ItemPointerSetInvalid(&(erm->curCtid));
continue;
}
}
erm->ermActive = true;
/* fetch the tuple's ctid */
datum = ExecGetJunkAttribute(slot,
aerm->ctidAttNo,
&isNull);
/* shouldn't ever get a null result... */
if (isNull)
elog(ERROR, "ctid is NULL");
/* requests for foreign tables must be passed to their FDW */
if (erm->relation->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
{
FdwRoutine *fdwroutine;
bool updated = false;
fdwroutine = GetFdwRoutineForRelation(erm->relation, false);
/* this should have been checked already, but let's be safe */
if (fdwroutine->RefetchForeignRow == NULL)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot lock rows in foreign table \"%s\"",
RelationGetRelationName(erm->relation))));
copyTuple = fdwroutine->RefetchForeignRow(estate,
erm,
datum,
&updated);
if (copyTuple == NULL)
{
/* couldn't get the lock, so skip this row */ goto lnext;
}
/* save locked tuple for possible EvalPlanQual testing below */
*testTuple = copyTuple;
/*
* if FDW says tuple was updated before getting locked, we need to
* perform EPQ testing to see if quals are still satisfied
*/
if (updated)
epq_needed = true;
continue;
}
/* okay, try to lock the tuple */
tuple.t_self = *((ItemPointer) DatumGetPointer(datum));
switch (erm->markType)
{
case ROW_MARK_EXCLUSIVE:
lockmode = LockTupleExclusive;
break;
case ROW_MARK_NOKEYEXCLUSIVE:
lockmode = LockTupleNoKeyExclusive;
break;
case ROW_MARK_SHARE:
lockmode = LockTupleShare;
break;
case ROW_MARK_KEYSHARE:
lockmode = LockTupleKeyShare;
break;
default:
elog(ERROR, "unsupported rowmark type");
lockmode = LockTupleNoKeyExclusive; /* keep compiler quiet */
break;
}
test = heap_lock_tuple(erm->relation, &tuple,
estate->es_output_cid,
lockmode, erm->waitPolicy, true,
&buffer, &hufd);
ReleaseBuffer(buffer);
switch (test)
{
case HeapTupleWouldBlock:
/* couldn't lock tuple in SKIP LOCKED mode */
goto lnext;
case HeapTupleSelfUpdated:
/*
* The target tuple was already updated or deleted by the
* current command, or by a later command in the current
* transaction. We *must* ignore the tuple in the former
* case, so as to avoid the "Halloween problem" of repeated
* update attempts. In the latter case it might be sensible
* to fetch the updated tuple instead, but doing so would
* require changing heap_update and heap_delete to not
* complain about updating "invisible" tuples, which seems
* pretty scary (heap_lock_tuple will not complain, but few
* callers expect HeapTupleInvisible, and we're not one of
* them). So for now, treat the tuple as deleted and do not
* process.
*/
goto lnext;
case HeapTupleMayBeUpdated:
/* got the lock successfully */
break;
case HeapTupleUpdated:
if (IsolationUsesXactSnapshot())
ereport(ERROR,
(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
errmsg("could not serialize access due to concurrent update")));
if (ItemPointerEquals(&hufd.ctid, &tuple.t_self))
{
/* Tuple was deleted, so don't return it */
goto lnext;
}
/* updated, so fetch and lock the updated version */
copyTuple = EvalPlanQualFetch(estate, erm->relation,
lockmode, erm->waitPolicy,
&hufd.ctid, hufd.xmax);
if (copyTuple == NULL)
{
/*
* Tuple was deleted; or it's locked and we're under SKIP
* LOCKED policy, so don't return it
*/
goto lnext;
}
/* remember the actually locked tuple's TID */
tuple.t_self = copyTuple->t_self;
/* Save locked tuple for EvalPlanQual testing below */
*testTuple = copyTuple;
/* Remember we need to do EPQ testing */
epq_needed = true;
/* Continue loop until we have all target tuples */
break;
case HeapTupleInvisible:
elog(ERROR, "attempted to lock invisible tuple");
default:
elog(ERROR, "unrecognized heap_lock_tuple status: %u",
test);
}
/* Remember locked tuple's TID for EPQ testing and WHERE CURRENT OF */
erm->curCtid = tuple.t_self;
}
/*
* If we need to do EvalPlanQual testing, do so.
*/
if (epq_needed)
{
int i;
/* Initialize EPQ machinery */
EvalPlanQualBegin(&node->lr_epqstate, estate);
/*
* Transfer already-fetched tuples into the EPQ state, and make sure
* its test tuples for other tables are reset to NULL.
*/
for (i = 0; i < node->lr_ntables; i++)
{
EvalPlanQualSetTuple(&node->lr_epqstate,
i + 1,
node->lr_curtuples[i]);
/* freeing this tuple is now the responsibility of EPQ */
node->lr_curtuples[i] = NULL; }
/*
* Next, fetch a copy of any rows that were successfully locked
* without any update having occurred. (We do this in a separate pass
* so as to avoid overhead in the common case where there are no
* concurrent updates.)
*/
foreach(lc, node->lr_arowMarks)
{
ExecAuxRowMark *aerm = (ExecAuxRowMark *) lfirst(lc);
ExecRowMark *erm = aerm->rowmark;
HeapTupleData tuple;
Buffer buffer;
/* ignore non-active child tables */
if (!erm->ermActive)
{
Assert(erm->rti != erm->prti); /* check it's child table */
continue;
}
if (EvalPlanQualGetTuple(&node->lr_epqstate, erm->rti) != NULL)
continue; /* it was updated and fetched above */
/* foreign tables should have been fetched above */
Assert(erm->relation->rd_rel->relkind != RELKIND_FOREIGN_TABLE);
Assert(ItemPointerIsValid(&(erm->curCtid)));
/* okay, fetch the tuple */
tuple.t_self = erm->curCtid;
if (!heap_fetch(erm->relation, SnapshotAny, &tuple, &buffer,
false, NULL))
elog(ERROR, "failed to fetch tuple for EvalPlanQual recheck");
/* successful, copy and store tuple */
EvalPlanQualSetTuple(&node->lr_epqstate, erm->rti,
heap_copytuple(&tuple));
ReleaseBuffer(buffer);
}
/*
* Now fetch any non-locked source rows --- the EPQ logic knows how to
* do that.
*/
EvalPlanQualSetSlot(&node->lr_epqstate, slot);
EvalPlanQualFetchRowMarks(&node->lr_epqstate);
/*
* And finally we can re-evaluate the tuple.
*/
slot = EvalPlanQualNext(&node->lr_epqstate);
if (TupIsNull(slot))
{
/* Updated tuple fails qual, so ignore it and go on */
goto lnext;
}
}
/* Got all locks, so return the current tuple */
return slot;
}
/* ----------------------------------------------------------------
* ExecInitLockRows
*
* This initializes the LockRows node state structures and
* the node's subplan.
* ----------------------------------------------------------------
*/LockRowsState *
ExecInitLockRows(LockRows *node, EState *estate, int eflags)
{
LockRowsState *lrstate;
Plan *outerPlan = outerPlan(node);
List *epq_arowmarks;
ListCell *lc;
/* check for unsupported flags */
Assert(!(eflags & EXEC_FLAG_MARK));
/*
* create state structure
*/
lrstate = makeNode(LockRowsState);
lrstate->ps.plan = (Plan *) node;
lrstate->ps.state = estate;
/*
* Miscellaneous initialization
*
* LockRows nodes never call ExecQual or ExecProject.
*/
/*
* Tuple table initialization (XXX not actually used...)
*/
ExecInitResultTupleSlot(estate, &lrstate->ps);
/*
* then initialize outer plan
*/
outerPlanState(lrstate) = ExecInitNode(outerPlan, estate, eflags);
/*
* LockRows nodes do no projections, so initialize projection info for
* this node appropriately
*/
ExecAssignResultTypeFromTL(&lrstate->ps);
lrstate->ps.ps_ProjInfo = NULL;
/*
* Create workspace in which we can remember per-RTE locked tuples
*/
lrstate->lr_ntables = list_length(estate->es_range_table);
lrstate->lr_curtuples = (HeapTuple *)
palloc0(lrstate->lr_ntables * sizeof(HeapTuple));
/*
* Locate the ExecRowMark(s) that this node is responsible for, and
* construct ExecAuxRowMarks for them. (InitPlan should already have
* built the global list of ExecRowMarks.)
*/
lrstate->lr_arowMarks = NIL;
epq_arowmarks = NIL;
foreach(lc, node->rowMarks)
{
PlanRowMark *rc = (PlanRowMark *) lfirst(lc);
ExecRowMark *erm;
ExecAuxRowMark *aerm;
Assert(IsA(rc, PlanRowMark));
/* ignore "parent" rowmarks; they are irrelevant at runtime */
if (rc->isParent)
continue;
/* safety check on size of lr_curtuples array */
Assert(rc->rti > 0 && rc->rti <= lrstate->lr_ntables);
/* find ExecRowMark and build ExecAuxRowMark */
erm = ExecFindRowMark(estate, rc->rti, false);
aerm = ExecBuildAuxRowMark(erm, outerPlan->targetlist);
/*
* Only locking rowmarks go into our own list. Non-locking marks are
* passed off to the EvalPlanQual machinery. This is because we don't
* want to bother fetching non-locked rows unless we actually have to
* do an EPQ recheck.
*/
if (RowMarkRequiresRowShareLock(erm->markType))
lrstate->lr_arowMarks = lappend(lrstate->lr_arowMarks, aerm);
else
epq_arowmarks = lappend(epq_arowmarks, aerm);
}
/* Now we have the info needed to set up EPQ state */
EvalPlanQualInit(&lrstate->lr_epqstate, estate,
outerPlan, epq_arowmarks, node->epqParam);
return lrstate;
}
/* ----------------------------------------------------------------
* ExecEndLockRows
*
* This shuts down the subplan and frees resources allocated
* to this node.
* ----------------------------------------------------------------
*/
void
ExecEndLockRows(LockRowsState *node)
{
EvalPlanQualEnd(&node->lr_epqstate);
ExecEndNode(outerPlanState(node));
}
void
ExecReScanLockRows(LockRowsState *node)
{
/*
* if chgParam of subnode is not null then plan will be re-scanned by
* first ExecProcNode.
*/
if (node->ps.lefttree->chgParam == NULL)
ExecReScan(node->ps.lefttree);
}