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Commitcb5b286

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Fix bug in Tid scan.
Commit147e372 changed Tid scan so that it calls table_beginscan()and uses the scan option for seq scan. This change caused two issues.(1) The change caused Tid scan to take a predicate lock on the entire relation in serializable transaction even when relation-level lock is not necessary. This could lead to an unexpected serialization error.(2) The change caused Tid scan to increment the number of seq_scan in pg_stat_*_tables views even though it's not seq scan. This could confuse the users.This commit adds the scan option for Tid scan and makes Tid scanuse it, to avoid those issues.Back-patch to v12, where the bug was introduced.Author: Tatsuhito KasaharaReviewed-by: Kyotaro Horiguchi, Masahiko Sawada, Fujii MasaoDiscussion:https://postgr.es/m/CAP0=ZVKy+gTbFmB6X_UW0pP3WaeJ-fkUWHoD-pExS=at3CY76g@mail.gmail.com
1 parentb059d2f commitcb5b286

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5 files changed

+46
-10
lines changed

5 files changed

+46
-10
lines changed

‎src/backend/executor/nodeTidscan.c‎

Lines changed: 2 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -143,9 +143,8 @@ TidListEval(TidScanState *tidstate)
143143
*/
144144
if (tidstate->ss.ss_currentScanDesc==NULL)
145145
tidstate->ss.ss_currentScanDesc=
146-
table_beginscan(tidstate->ss.ss_currentRelation,
147-
tidstate->ss.ps.state->es_snapshot,
148-
0,NULL);
146+
table_beginscan_tid(tidstate->ss.ss_currentRelation,
147+
tidstate->ss.ps.state->es_snapshot);
149148
scan=tidstate->ss.ss_currentScanDesc;
150149

151150
/*

‎src/backend/utils/adt/tid.c‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -381,7 +381,7 @@ currtid_byreloid(PG_FUNCTION_ARGS)
381381
ItemPointerCopy(tid,result);
382382

383383
snapshot=RegisterSnapshot(GetLatestSnapshot());
384-
scan=table_beginscan(rel,snapshot,0,NULL);
384+
scan=table_beginscan_tid(rel,snapshot);
385385
table_tuple_get_latest_tid(scan,result);
386386
table_endscan(scan);
387387
UnregisterSnapshot(snapshot);
@@ -419,7 +419,7 @@ currtid_byrelname(PG_FUNCTION_ARGS)
419419
ItemPointerCopy(tid,result);
420420

421421
snapshot=RegisterSnapshot(GetLatestSnapshot());
422-
scan=table_beginscan(rel,snapshot,0,NULL);
422+
scan=table_beginscan_tid(rel,snapshot);
423423
table_tuple_get_latest_tid(scan,result);
424424
table_endscan(scan);
425425
UnregisterSnapshot(snapshot);

‎src/include/access/tableam.h‎

Lines changed: 19 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -47,18 +47,19 @@ typedef enum ScanOptions
4747
SO_TYPE_SEQSCAN=1 <<0,
4848
SO_TYPE_BITMAPSCAN=1 <<1,
4949
SO_TYPE_SAMPLESCAN=1 <<2,
50-
SO_TYPE_ANALYZE=1 <<3,
50+
SO_TYPE_TIDSCAN=1 <<3,
51+
SO_TYPE_ANALYZE=1 <<4,
5152

5253
/* several of SO_ALLOW_* may be specified */
5354
/* allow or disallow use of access strategy */
54-
SO_ALLOW_STRAT=1 <<4,
55+
SO_ALLOW_STRAT=1 <<5,
5556
/* report location to syncscan logic? */
56-
SO_ALLOW_SYNC=1 <<5,
57+
SO_ALLOW_SYNC=1 <<6,
5758
/* verify visibility page-at-a-time? */
58-
SO_ALLOW_PAGEMODE=1 <<6,
59+
SO_ALLOW_PAGEMODE=1 <<7,
5960

6061
/* unregister snapshot at scan end? */
61-
SO_TEMP_SNAPSHOT=1 <<7
62+
SO_TEMP_SNAPSHOT=1 <<8
6263
}ScanOptions;
6364

6465
/*
@@ -829,6 +830,19 @@ table_beginscan_sampling(Relation rel, Snapshot snapshot,
829830
returnrel->rd_tableam->scan_begin(rel,snapshot,nkeys,key,NULL,flags);
830831
}
831832

833+
/*
834+
* table_beginscan_tid is an alternative entry point for setting up a
835+
* TableScanDesc for a Tid scan. As with bitmap scans, it's worth using
836+
* the same data structure although the behavior is rather different.
837+
*/
838+
staticinlineTableScanDesc
839+
table_beginscan_tid(Relationrel,Snapshotsnapshot)
840+
{
841+
uint32flags=SO_TYPE_TIDSCAN;
842+
843+
returnrel->rd_tableam->scan_begin(rel,snapshot,0,NULL,NULL,flags);
844+
}
845+
832846
/*
833847
* table_beginscan_analyze is an alternative entry point for setting up a
834848
* TableScanDesc for an ANALYZE scan. As with bitmap scans, it's worth using

‎src/test/regress/expected/tidscan.out‎

Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -277,4 +277,20 @@ SELECT count(*) FROM tenk1 t1 JOIN tenk1 t2 ON t1.ctid = t2.ctid;
277277
(1 row)
278278

279279
RESET enable_hashjoin;
280+
-- check predicate lock on CTID
281+
BEGIN ISOLATION LEVEL SERIALIZABLE;
282+
SELECT * FROM tidscan WHERE ctid = '(0,1)';
283+
id
284+
----
285+
1
286+
(1 row)
287+
288+
-- locktype should be 'tuple'
289+
SELECT locktype, mode FROM pg_locks WHERE pid = pg_backend_pid() AND mode = 'SIReadLock';
290+
locktype | mode
291+
----------+------------
292+
tuple | SIReadLock
293+
(1 row)
294+
295+
ROLLBACK;
280296
DROP TABLE tidscan;

‎src/test/regress/sql/tidscan.sql‎

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -94,4 +94,11 @@ SELECT count(*) FROM tenk1 t1 JOIN tenk1 t2 ON t1.ctid = t2.ctid;
9494
SELECTcount(*)FROM tenk1 t1JOIN tenk1 t2ONt1.ctid=t2.ctid;
9595
RESET enable_hashjoin;
9696

97+
-- check predicate lock on CTID
98+
BEGIN ISOLATION LEVEL SERIALIZABLE;
99+
SELECT*FROM tidscanWHERE ctid='(0,1)';
100+
-- locktype should be 'tuple'
101+
SELECT locktype, modeFROM pg_locksWHERE pid= pg_backend_pid()AND mode='SIReadLock';
102+
ROLLBACK;
103+
97104
DROPTABLE tidscan;

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