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tableam: Avoid relying on relation size to determine validity of tids.

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Instead add a tableam callback to do so. To avoid adding per
validation overhead, pass a scan to tuple_tid_valid. In heap's case
we'd otherwise incurred a RelationGetNumberOfBlocks() call for each
tid - which'd have added noticable overhead to nodeTidscan.c.

Author: Andres Freund
Reviewed-By: Ashwin Agrawal
Discussion: https://postgr.es/m/20190515185447.gno2jtqxyktylyvs@alap3.anarazel.de
This commit is contained in:
Andres Freund
2019-05-17 18:52:01 -07:00
parent 7f44ede594
commit 147e3722f7
7 changed files with 129 additions and 57 deletions
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73
src/backend/executor/nodeTidscan.c
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@ -129,19 +129,23 @@ static void
TidListEval(TidScanState *tidstate)
{
ExprContext *econtext = tidstate->ss.ps.ps_ExprContext;
BlockNumber nblocks;
TableScanDesc scan;
ItemPointerData *tidList;
int numAllocTids;
int numTids;
ListCell *l;
/*
* We silently discard any TIDs that are out of range at the time of scan
* start. (Since we hold at least AccessShareLock on the table, it won't
* be possible for someone to truncate away the blocks we intend to
* visit.)
* Start scan on-demand - initializing a scan isn't free (e.g. heap stats
* the size of the table), so it makes sense to delay that until needed -
* the node might never get executed.
*/
nblocks = RelationGetNumberOfBlocks(tidstate->ss.ss_currentRelation);
if (tidstate->ss.ss_currentScanDesc == NULL)
tidstate->ss.ss_currentScanDesc =
table_beginscan(tidstate->ss.ss_currentRelation,
tidstate->ss.ps.state->es_snapshot,
0, NULL);
scan = tidstate->ss.ss_currentScanDesc;
/*
* We initialize the array with enough slots for the case that all quals
@ -165,19 +169,27 @@ TidListEval(TidScanState *tidstate)
DatumGetPointer(ExecEvalExprSwitchContext(tidexpr->exprstate,
econtext,
&isNull));
if (!isNull &&
ItemPointerIsValid(itemptr) &&
ItemPointerGetBlockNumber(itemptr) < nblocks)
if (isNull)
continue;
/*
* We silently discard any TIDs that the AM considers invalid
* (E.g. for heap, they could be out of range at the time of scan
* start. Since we hold at least AccessShareLock on the table, it
* won't be possible for someone to truncate away the blocks we
* intend to visit.).
*/
if (!table_tuple_tid_valid(scan, itemptr))
continue;
if (numTids >= numAllocTids)
{
if (numTids >= numAllocTids)
{
numAllocTids *= 2;
tidList = (ItemPointerData *)
repalloc(tidList,
numAllocTids * sizeof(ItemPointerData));
}
tidList[numTids++] = *itemptr;
numAllocTids *= 2;
tidList = (ItemPointerData *)
repalloc(tidList,
numAllocTids * sizeof(ItemPointerData));
}
tidList[numTids++] = *itemptr;
}
else if (tidexpr->exprstate && tidexpr->isarray)
{
@ -206,13 +218,15 @@ TidListEval(TidScanState *tidstate)
}
for (i = 0; i < ndatums; i++)
{
if (!ipnulls[i])
{
itemptr = (ItemPointer) DatumGetPointer(ipdatums[i]);
if (ItemPointerIsValid(itemptr) &&
ItemPointerGetBlockNumber(itemptr) < nblocks)
tidList[numTids++] = *itemptr;
}
if (ipnulls[i])
continue;
itemptr = (ItemPointer) DatumGetPointer(ipdatums[i]);
if (!table_tuple_tid_valid(scan, itemptr))
continue;
tidList[numTids++] = *itemptr;
}
pfree(ipdatums);
pfree(ipnulls);
@ -306,6 +320,7 @@ TidNext(TidScanState *node)
EState *estate;
ScanDirection direction;
Snapshot snapshot;
TableScanDesc scan;
Relation heapRelation;
TupleTableSlot *slot;
ItemPointerData *tidList;
@ -327,6 +342,7 @@ TidNext(TidScanState *node)
if (node->tss_TidList == NULL)
TidListEval(node);
scan = node->ss.ss_currentScanDesc;
tidList = node->tss_TidList;
numTids = node->tss_NumTids;
@ -365,7 +381,7 @@ TidNext(TidScanState *node)
* current according to our snapshot.
*/
if (node->tss_isCurrentOf)
table_get_latest_tid(heapRelation, snapshot, &tid);
table_get_latest_tid(scan, &tid);
if (table_fetch_row_version(heapRelation, &tid, snapshot, slot))
return slot;
@ -442,6 +458,10 @@ ExecReScanTidScan(TidScanState *node)
node->tss_NumTids = 0;
node->tss_TidPtr = -1;
/* not really necessary, but seems good form */
if (node->ss.ss_currentScanDesc)
table_rescan(node->ss.ss_currentScanDesc, NULL);
ExecScanReScan(&node->ss);
}
@ -455,6 +475,9 @@ ExecReScanTidScan(TidScanState *node)
void
ExecEndTidScan(TidScanState *node)
{
if (node->ss.ss_currentScanDesc)
table_endscan(node->ss.ss_currentScanDesc);
/*
* Free the exprcontext
*/