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Commit147e372

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tableam: Avoid relying on relation size to determine validity of tids.
Instead add a tableam callback to do so. To avoid adding pervalidation overhead, pass a scan to tuple_tid_valid. In heap's casewe'd otherwise incurred a RelationGetNumberOfBlocks() call for eachtid - which'd have added noticable overhead to nodeTidscan.c.Author: Andres FreundReviewed-By: Ashwin AgrawalDiscussion:https://postgr.es/m/20190515185447.gno2jtqxyktylyvs@alap3.anarazel.de
1 parent7f44ede commit147e372

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7 files changed

+129
-57
lines changed

7 files changed

+129
-57
lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 9 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -1654,37 +1654,29 @@ heap_hot_search_buffer(ItemPointer tid, Relation relation, Buffer buffer,
16541654
/*
16551655
*heap_get_latest_tid - get the latest tid of a specified tuple
16561656
*
1657-
* Actually, this gets the latest version that is visible according to
1658-
*the passedsnapshot.You can pass SnapshotDirty to get the very latest,
1657+
* Actually, this gets the latest version that is visible according to the
1658+
*scan'ssnapshot.Create a scan using SnapshotDirty to get the very latest,
16591659
* possibly uncommitted version.
16601660
*
16611661
* *tid is both an input and an output parameter: it is updated to
16621662
* show the latest version of the row. Note that it will not be changed
16631663
* if no version of the row passes the snapshot test.
16641664
*/
16651665
void
1666-
heap_get_latest_tid(Relationrelation,
1667-
Snapshotsnapshot,
1666+
heap_get_latest_tid(TableScanDescsscan,
16681667
ItemPointertid)
16691668
{
1670-
BlockNumberblk;
1669+
Relationrelation=sscan->rs_rd;
1670+
Snapshotsnapshot=sscan->rs_snapshot;
16711671
ItemPointerDatactid;
16721672
TransactionIdpriorXmax;
16731673

1674-
/* this is to avoid Assert failures on bad input */
1675-
if (!ItemPointerIsValid(tid))
1676-
return;
1677-
16781674
/*
1679-
* Since this can be called with user-supplied TID, don't trust the input
1680-
* too much. (RelationGetNumberOfBlocks is an expensive check, so we
1681-
* don't check t_ctid links again this way. Note that it would not do to
1682-
* call it just once and save the result, either.)
1675+
* table_get_latest_tid verified that the passed in tid is valid. Assume
1676+
* that t_ctid links are valid however - there shouldn't be invalid ones
1677+
* in the table.
16831678
*/
1684-
blk=ItemPointerGetBlockNumber(tid);
1685-
if (blk >=RelationGetNumberOfBlocks(relation))
1686-
elog(ERROR,"block number %u is out of range for relation \"%s\"",
1687-
blk,RelationGetRelationName(relation));
1679+
Assert(ItemPointerIsValid(tid));
16881680

16891681
/*
16901682
* Loop to chase down t_ctid links. At top of loop, ctid is the tuple we

‎src/backend/access/heap/heapam_handler.c

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -204,6 +204,15 @@ heapam_fetch_row_version(Relation relation,
204204
return false;
205205
}
206206

207+
staticbool
208+
heapam_tuple_tid_valid(TableScanDescscan,ItemPointertid)
209+
{
210+
HeapScanDeschscan= (HeapScanDesc)scan;
211+
212+
returnItemPointerIsValid(tid)&&
213+
ItemPointerGetBlockNumber(tid)<hscan->rs_nblocks;
214+
}
215+
207216
staticbool
208217
heapam_tuple_satisfies_snapshot(Relationrel,TupleTableSlot*slot,
209218
Snapshotsnapshot)
@@ -2568,6 +2577,7 @@ static const TableAmRoutine heapam_methods = {
25682577

25692578
.tuple_fetch_row_version=heapam_fetch_row_version,
25702579
.tuple_get_latest_tid=heap_get_latest_tid,
2580+
.tuple_tid_valid=heapam_tuple_tid_valid,
25712581
.tuple_satisfies_snapshot=heapam_tuple_satisfies_snapshot,
25722582
.compute_xid_horizon_for_tuples=heap_compute_xid_horizon_for_tuples,
25732583

‎src/backend/access/table/tableam.c

Lines changed: 27 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -213,6 +213,33 @@ table_index_fetch_tuple_check(Relation rel,
213213
}
214214

215215

216+
/* ------------------------------------------------------------------------
217+
* Functions for non-modifying operations on individual tuples
218+
* ------------------------------------------------------------------------
219+
*/
220+
221+
void
222+
table_get_latest_tid(TableScanDescscan,ItemPointertid)
223+
{
224+
Relationrel=scan->rs_rd;
225+
constTableAmRoutine*tableam=rel->rd_tableam;
226+
227+
/*
228+
* Since this can be called with user-supplied TID, don't trust the input
229+
* too much.
230+
*/
231+
if (!tableam->tuple_tid_valid(scan,tid))
232+
ereport(ERROR,
233+
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
234+
errmsg("tid (%u, %u) is not valid for relation for relation \"%s\"",
235+
ItemPointerGetBlockNumberNoCheck(tid),
236+
ItemPointerGetOffsetNumberNoCheck(tid),
237+
RelationGetRelationName(rel))));
238+
239+
returntableam->tuple_get_latest_tid(scan,tid);
240+
}
241+
242+
216243
/* ----------------------------------------------------------------------------
217244
* Functions to make modifications a bit simpler.
218245
* ----------------------------------------------------------------------------

‎src/backend/executor/nodeTidscan.c

Lines changed: 48 additions & 25 deletions
Original file line numberDiff line numberDiff line change
@@ -129,19 +129,23 @@ static void
129129
TidListEval(TidScanState*tidstate)
130130
{
131131
ExprContext*econtext=tidstate->ss.ps.ps_ExprContext;
132-
BlockNumbernblocks;
132+
TableScanDescscan;
133133
ItemPointerData*tidList;
134134
intnumAllocTids;
135135
intnumTids;
136136
ListCell*l;
137137

138138
/*
139-
* We silently discard any TIDs that are out of range at the time of scan
140-
* start. (Since we hold at least AccessShareLock on the table, it won't
141-
* be possible for someone to truncate away the blocks we intend to
142-
* visit.)
139+
* Start scan on-demand - initializing a scan isn't free (e.g. heap stats
140+
* the size of the table), so it makes sense to delay that until needed -
141+
* the node might never get executed.
143142
*/
144-
nblocks=RelationGetNumberOfBlocks(tidstate->ss.ss_currentRelation);
143+
if (tidstate->ss.ss_currentScanDesc==NULL)
144+
tidstate->ss.ss_currentScanDesc=
145+
table_beginscan(tidstate->ss.ss_currentRelation,
146+
tidstate->ss.ps.state->es_snapshot,
147+
0,NULL);
148+
scan=tidstate->ss.ss_currentScanDesc;
145149

146150
/*
147151
* We initialize the array with enough slots for the case that all quals
@@ -165,19 +169,27 @@ TidListEval(TidScanState *tidstate)
165169
DatumGetPointer(ExecEvalExprSwitchContext(tidexpr->exprstate,
166170
econtext,
167171
&isNull));
168-
if (!isNull&&
169-
ItemPointerIsValid(itemptr)&&
170-
ItemPointerGetBlockNumber(itemptr)<nblocks)
172+
if (isNull)
173+
continue;
174+
175+
/*
176+
* We silently discard any TIDs that the AM considers invalid
177+
* (E.g. for heap, they could be out of range at the time of scan
178+
* start. Since we hold at least AccessShareLock on the table, it
179+
* won't be possible for someone to truncate away the blocks we
180+
* intend to visit.).
181+
*/
182+
if (!table_tuple_tid_valid(scan,itemptr))
183+
continue;
184+
185+
if (numTids >=numAllocTids)
171186
{
172-
if (numTids >=numAllocTids)
173-
{
174-
numAllocTids *=2;
175-
tidList= (ItemPointerData*)
176-
repalloc(tidList,
177-
numAllocTids*sizeof(ItemPointerData));
178-
}
179-
tidList[numTids++]=*itemptr;
187+
numAllocTids *=2;
188+
tidList= (ItemPointerData*)
189+
repalloc(tidList,
190+
numAllocTids*sizeof(ItemPointerData));
180191
}
192+
tidList[numTids++]=*itemptr;
181193
}
182194
elseif (tidexpr->exprstate&&tidexpr->isarray)
183195
{
@@ -206,13 +218,15 @@ TidListEval(TidScanState *tidstate)
206218
}
207219
for (i=0;i<ndatums;i++)
208220
{
209-
if (!ipnulls[i])
210-
{
211-
itemptr= (ItemPointer)DatumGetPointer(ipdatums[i]);
212-
if (ItemPointerIsValid(itemptr)&&
213-
ItemPointerGetBlockNumber(itemptr)<nblocks)
214-
tidList[numTids++]=*itemptr;
215-
}
221+
if (ipnulls[i])
222+
continue;
223+
224+
itemptr= (ItemPointer)DatumGetPointer(ipdatums[i]);
225+
226+
if (!table_tuple_tid_valid(scan,itemptr))
227+
continue;
228+
229+
tidList[numTids++]=*itemptr;
216230
}
217231
pfree(ipdatums);
218232
pfree(ipnulls);
@@ -306,6 +320,7 @@ TidNext(TidScanState *node)
306320
EState*estate;
307321
ScanDirectiondirection;
308322
Snapshotsnapshot;
323+
TableScanDescscan;
309324
RelationheapRelation;
310325
TupleTableSlot*slot;
311326
ItemPointerData*tidList;
@@ -327,6 +342,7 @@ TidNext(TidScanState *node)
327342
if (node->tss_TidList==NULL)
328343
TidListEval(node);
329344

345+
scan=node->ss.ss_currentScanDesc;
330346
tidList=node->tss_TidList;
331347
numTids=node->tss_NumTids;
332348

@@ -365,7 +381,7 @@ TidNext(TidScanState *node)
365381
* current according to our snapshot.
366382
*/
367383
if (node->tss_isCurrentOf)
368-
table_get_latest_tid(heapRelation,snapshot,&tid);
384+
table_get_latest_tid(scan,&tid);
369385

370386
if (table_fetch_row_version(heapRelation,&tid,snapshot,slot))
371387
returnslot;
@@ -442,6 +458,10 @@ ExecReScanTidScan(TidScanState *node)
442458
node->tss_NumTids=0;
443459
node->tss_TidPtr=-1;
444460

461+
/* not really necessary, but seems good form */
462+
if (node->ss.ss_currentScanDesc)
463+
table_rescan(node->ss.ss_currentScanDesc,NULL);
464+
445465
ExecScanReScan(&node->ss);
446466
}
447467

@@ -455,6 +475,9 @@ ExecReScanTidScan(TidScanState *node)
455475
void
456476
ExecEndTidScan(TidScanState*node)
457477
{
478+
if (node->ss.ss_currentScanDesc)
479+
table_endscan(node->ss.ss_currentScanDesc);
480+
458481
/*
459482
* Free the exprcontext
460483
*/

‎src/backend/utils/adt/tid.c

Lines changed: 8 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -358,6 +358,7 @@ currtid_byreloid(PG_FUNCTION_ARGS)
358358
Relationrel;
359359
AclResultaclresult;
360360
Snapshotsnapshot;
361+
TableScanDescscan;
361362

362363
result= (ItemPointer)palloc(sizeof(ItemPointerData));
363364
if (!reloid)
@@ -380,7 +381,9 @@ currtid_byreloid(PG_FUNCTION_ARGS)
380381
ItemPointerCopy(tid,result);
381382

382383
snapshot=RegisterSnapshot(GetLatestSnapshot());
383-
table_get_latest_tid(rel,snapshot,result);
384+
scan=table_beginscan(rel,snapshot,0,NULL);
385+
table_get_latest_tid(scan,result);
386+
table_endscan(scan);
384387
UnregisterSnapshot(snapshot);
385388

386389
table_close(rel,AccessShareLock);
@@ -398,6 +401,7 @@ currtid_byrelname(PG_FUNCTION_ARGS)
398401
Relationrel;
399402
AclResultaclresult;
400403
Snapshotsnapshot;
404+
TableScanDescscan;
401405

402406
relrv=makeRangeVarFromNameList(textToQualifiedNameList(relname));
403407
rel=table_openrv(relrv,AccessShareLock);
@@ -415,7 +419,9 @@ currtid_byrelname(PG_FUNCTION_ARGS)
415419
ItemPointerCopy(tid,result);
416420

417421
snapshot=RegisterSnapshot(GetLatestSnapshot());
418-
table_get_latest_tid(rel,snapshot,result);
422+
scan=table_beginscan(rel,snapshot,0,NULL);
423+
table_get_latest_tid(scan,result);
424+
table_endscan(scan);
419425
UnregisterSnapshot(snapshot);
420426

421427
table_close(rel,AccessShareLock);

‎src/include/access/heapam.h

Lines changed: 1 addition & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -134,8 +134,7 @@ extern bool heap_hot_search_buffer(ItemPointer tid, Relation relation,
134134
Bufferbuffer,Snapshotsnapshot,HeapTupleheapTuple,
135135
bool*all_dead,boolfirst_call);
136136

137-
externvoidheap_get_latest_tid(Relationrelation,Snapshotsnapshot,
138-
ItemPointertid);
137+
externvoidheap_get_latest_tid(TableScanDescscan,ItemPointertid);
139138
externvoidsetLastTid(constItemPointertid);
140139

141140
externBulkInsertStateGetBulkInsertState(void);

‎src/include/access/tableam.h

Lines changed: 26 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -308,12 +308,17 @@ typedef struct TableAmRoutine
308308
Snapshotsnapshot,
309309
TupleTableSlot*slot);
310310

311+
/*
312+
* Is tid valid for a scan of this relation.
313+
*/
314+
bool(*tuple_tid_valid) (TableScanDescscan,
315+
ItemPointertid);
316+
311317
/*
312318
* Return the latest version of the tuple at `tid`, by updating `tid` to
313319
* point at the newest version.
314320
*/
315-
void(*tuple_get_latest_tid) (Relationrel,
316-
Snapshotsnapshot,
321+
void(*tuple_get_latest_tid) (TableScanDescscan,
317322
ItemPointertid);
318323

319324
/*
@@ -548,10 +553,10 @@ typedef struct TableAmRoutine
548553
/*
549554
* See table_relation_size().
550555
*
551-
* Note that currently a few callers use the MAIN_FORKNUM size tovet the
552-
*validity of tids (e.g. nodeTidscans.c), and others use it to figure out
553-
*the range of potentially interesting blocks (brin, analyze). The
554-
*abstraction around this will need to be improved in the near future.
556+
* Note that currently a few callers use the MAIN_FORKNUM size tofigure
557+
*out the range of potentially interesting blocks (brin, analyze). It's
558+
*probable that we'll need to revise the interface for those at some
559+
*point.
555560
*/
556561
uint64(*relation_size) (Relationrel,ForkNumberforkNumber);
557562

@@ -986,15 +991,25 @@ table_fetch_row_version(Relation rel,
986991
}
987992

988993
/*
989-
* Return the latest version of the tuple at `tid`, by updating `tid` to
990-
* point at the newest version.
994+
* Verify that `tid` is a potentially valid tuple identifier. That doesn't
995+
* mean that the pointed to row needs to exist or be visible, but that
996+
* attempting to fetch the row (e.g. with table_get_latest_tid() or
997+
* table_fetch_row_version()) should not error out if called with that tid.
998+
*
999+
* `scan` needs to have been started via table_beginscan().
9911000
*/
992-
staticinlinevoid
993-
table_get_latest_tid(Relationrel,Snapshotsnapshot,ItemPointertid)
1001+
staticinlinebool
1002+
table_tuple_tid_valid(TableScanDescscan,ItemPointertid)
9941003
{
995-
rel->rd_tableam->tuple_get_latest_tid(rel,snapshot,tid);
1004+
returnscan->rs_rd->rd_tableam->tuple_tid_valid(scan,tid);
9961005
}
9971006

1007+
/*
1008+
* Return the latest version of the tuple at `tid`, by updating `tid` to
1009+
* point at the newest version.
1010+
*/
1011+
externvoidtable_get_latest_tid(TableScanDescscan,ItemPointertid);
1012+
9981013
/*
9991014
* Return true iff tuple in slot satisfies the snapshot.
10001015
*

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