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Avoid O(N^2) cost in ExecFindRowMark().

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If there are many ExecRowMark structs, we spent O(N^2) time in
ExecFindRowMark during executor startup.  Once upon a time this was
not of great concern, but the addition of native partitioning has
squeezed out enough other costs that this can become the dominant
overhead in some use-cases for tables with many partitions.

To fix, simply replace that List data structure with an array.

This adds a little bit of cost to execCurrentOf(), but not much,
and anyway that code path is neither of large importance nor very
efficient now.  If we ever decide it is a bottleneck, constructing a
hash table for lookup-by-tableoid would likely be the thing to do.

Per complaint from Amit Langote, though this is different from
his fix proposal.

Discussion: https://postgr.es/m/468c85d9-540e-66a2-1dde-fec2b741e688@lab.ntt.co.jp
This commit is contained in:
Tom Lane
2018-10-08 10:41:34 -04:00
parent eee01d606e
commit f9eb7c14b0
4 changed files with 84 additions and 69 deletions
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11
src/backend/executor/execCurrent.c
View File

@@ -91,21 +91,22 @@ execCurrentOf(CurrentOfExpr *cexpr,
* the other code can't, while the non-FOR-UPDATE case allows use of WHERE
* CURRENT OF with an insensitive cursor.
*/
if (queryDesc->estate->es_rowMarks)
if (queryDesc->estate->es_rowmarks)
{
ExecRowMark *erm;
ListCell *lc;
Index i;
/*
* Here, the query must have exactly one FOR UPDATE/SHARE reference to
* the target table, and we dig the ctid info out of that.
*/
erm = NULL;
foreach(lc, queryDesc->estate->es_rowMarks)
for (i = 0; i < queryDesc->estate->es_range_table_size; i++)
{
ExecRowMark *thiserm = (ExecRowMark *) lfirst(lc);
ExecRowMark *thiserm = queryDesc->estate->es_rowmarks[i];
if (!RowMarkRequiresRowShareLock(thiserm->markType))
if (thiserm == NULL ||
!RowMarkRequiresRowShareLock(thiserm->markType))
continue; /* ignore non-FOR UPDATE/SHARE items */
if (thiserm->relid == table_oid)

120
src/backend/executor/execMain.c
View File

@@ -909,61 +909,68 @@ InitPlan(QueryDesc *queryDesc, int eflags)
}
/*
* Next, build the ExecRowMark list from the PlanRowMark(s), if any.
* Next, build the ExecRowMark array from the PlanRowMark(s), if any.
*/
estate->es_rowMarks = NIL;
foreach(l, plannedstmt->rowMarks)
if (plannedstmt->rowMarks)
{
PlanRowMark *rc = (PlanRowMark *) lfirst(l);
Oid relid;
Relation relation;
ExecRowMark *erm;
/* ignore "parent" rowmarks; they are irrelevant at runtime */
if (rc->isParent)
continue;
/* get relation's OID (will produce InvalidOid if subquery) */
relid = exec_rt_fetch(rc->rti, estate)->relid;
/* open relation, if we need to access it for this mark type */
switch (rc->markType)
estate->es_rowmarks = (ExecRowMark **)
palloc0(estate->es_range_table_size * sizeof(ExecRowMark *));
foreach(l, plannedstmt->rowMarks)
{
case ROW_MARK_EXCLUSIVE:
case ROW_MARK_NOKEYEXCLUSIVE:
case ROW_MARK_SHARE:
case ROW_MARK_KEYSHARE:
case ROW_MARK_REFERENCE:
relation = ExecGetRangeTableRelation(estate, rc->rti);
break;
case ROW_MARK_COPY:
/* no physical table access is required */
relation = NULL;
break;
default:
elog(ERROR, "unrecognized markType: %d", rc->markType);
relation = NULL; /* keep compiler quiet */
break;
PlanRowMark *rc = (PlanRowMark *) lfirst(l);
Oid relid;
Relation relation;
ExecRowMark *erm;
/* ignore "parent" rowmarks; they are irrelevant at runtime */
if (rc->isParent)
continue;
/* get relation's OID (will produce InvalidOid if subquery) */
relid = exec_rt_fetch(rc->rti, estate)->relid;
/* open relation, if we need to access it for this mark type */
switch (rc->markType)
{
case ROW_MARK_EXCLUSIVE:
case ROW_MARK_NOKEYEXCLUSIVE:
case ROW_MARK_SHARE:
case ROW_MARK_KEYSHARE:
case ROW_MARK_REFERENCE:
relation = ExecGetRangeTableRelation(estate, rc->rti);
break;
case ROW_MARK_COPY:
/* no physical table access is required */
relation = NULL;
break;
default:
elog(ERROR, "unrecognized markType: %d", rc->markType);
relation = NULL; /* keep compiler quiet */
break;
}
/* Check that relation is a legal target for marking */
if (relation)
CheckValidRowMarkRel(relation, rc->markType);
erm = (ExecRowMark *) palloc(sizeof(ExecRowMark));
erm->relation = relation;
erm->relid = relid;
erm->rti = rc->rti;
erm->prti = rc->prti;
erm->rowmarkId = rc->rowmarkId;
erm->markType = rc->markType;
erm->strength = rc->strength;
erm->waitPolicy = rc->waitPolicy;
erm->ermActive = false;
ItemPointerSetInvalid(&(erm->curCtid));
erm->ermExtra = NULL;
Assert(erm->rti > 0 && erm->rti <= estate->es_range_table_size &&
estate->es_rowmarks[erm->rti - 1] == NULL);
estate->es_rowmarks[erm->rti - 1] = erm;
}
/* Check that relation is a legal target for marking */
if (relation)
CheckValidRowMarkRel(relation, rc->markType);
erm = (ExecRowMark *) palloc(sizeof(ExecRowMark));
erm->relation = relation;
erm->relid = relid;
erm->rti = rc->rti;
erm->prti = rc->prti;
erm->rowmarkId = rc->rowmarkId;
erm->markType = rc->markType;
erm->strength = rc->strength;
erm->waitPolicy = rc->waitPolicy;
erm->ermActive = false;
ItemPointerSetInvalid(&(erm->curCtid));
erm->ermExtra = NULL;
estate->es_rowMarks = lappend(estate->es_rowMarks, erm);
}
/*
@@ -2394,13 +2401,12 @@ ExecUpdateLockMode(EState *estate, ResultRelInfo *relinfo)
ExecRowMark *
ExecFindRowMark(EState *estate, Index rti, bool missing_ok)
{
ListCell *lc;
foreach(lc, estate->es_rowMarks)
if (rti > 0 && rti <= estate->es_range_table_size &&
estate->es_rowmarks != NULL)
{
ExecRowMark *erm = (ExecRowMark *) lfirst(lc);
ExecRowMark *erm = estate->es_rowmarks[rti - 1];
if (erm->rti == rti)
if (erm)
return erm;
}
if (!missing_ok)
@@ -3131,6 +3137,7 @@ EvalPlanQualStart(EPQState *epqstate, EState *parentestate, Plan *planTree)
estate->es_range_table_array = parentestate->es_range_table_array;
estate->es_range_table_size = parentestate->es_range_table_size;
estate->es_relations = parentestate->es_relations;
estate->es_rowmarks = parentestate->es_rowmarks;
estate->es_plannedstmt = parentestate->es_plannedstmt;
estate->es_junkFilter = parentestate->es_junkFilter;
estate->es_output_cid = parentestate->es_output_cid;
@@ -3148,7 +3155,6 @@ EvalPlanQualStart(EPQState *epqstate, EState *parentestate, Plan *planTree)
}
/* es_result_relation_info must NOT be copied */
/* es_trig_target_relations must NOT be copied */
estate->es_rowMarks = parentestate->es_rowMarks;
estate->es_top_eflags = parentestate->es_top_eflags;
estate->es_instrument = parentestate->es_instrument;
/* es_auxmodifytables must NOT be copied */

9
src/backend/executor/execUtils.c
View File

@@ -113,6 +113,7 @@ CreateExecutorState(void)
estate->es_range_table_array = NULL;
estate->es_range_table_size = 0;
estate->es_relations = NULL;
estate->es_rowmarks = NULL;
estate->es_plannedstmt = NULL;
estate->es_junkFilter = NULL;
@@ -142,8 +143,6 @@ CreateExecutorState(void)
estate->es_tupleTable = NIL;
estate->es_rowMarks = NIL;
estate->es_processed = 0;
estate->es_lastoid = InvalidOid;
@@ -709,6 +708,12 @@ ExecInitRangeTable(EState *estate, List *rangeTable)
*/
estate->es_relations = (Relation *)
palloc0(estate->es_range_table_size * sizeof(Relation));
/*
* es_rowmarks is also parallel to the es_range_table_array, but it's
* allocated only if needed.
*/
estate->es_rowmarks = NULL;
}
/*