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Commit8f9b959

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Handle duplicate XIDs in txid_snapshot.
The proc array can contain duplicate XIDs, when a transaction is just beingprepared for two-phase commit. To cope, remove any duplicates intxid_current_snapshot(). Also ignore duplicates in the input functions, sothat if e.g. you have an old pg_dump file that already contains duplicates,it will be accepted.Report and fix by Jan Wieck. Backpatch to all supported versions.
1 parentbb38fb0 commit8f9b959

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3 files changed

+54
-17
lines changed

3 files changed

+54
-17
lines changed

‎src/backend/utils/adt/txid.c

Lines changed: 47 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -131,16 +131,34 @@ cmp_txid(const void *aa, const void *bb)
131131
}
132132

133133
/*
134-
* sort a snapshot's txids, so we can use bsearch() later.
134+
* Sort a snapshot's txids, so we can use bsearch() later. Also remove
135+
* any duplicates.
135136
*
136137
* For consistency of on-disk representation, we always sort even if bsearch
137138
* will not be used.
138139
*/
139140
staticvoid
140141
sort_snapshot(TxidSnapshot*snap)
141142
{
143+
txidlast=0;
144+
intnxip,idx1,idx2;
145+
142146
if (snap->nxip>1)
147+
{
143148
qsort(snap->xip,snap->nxip,sizeof(txid),cmp_txid);
149+
150+
/* remove duplicates */
151+
nxip=snap->nxip;
152+
idx1=idx2=0;
153+
while (idx1<nxip)
154+
{
155+
if (snap->xip[idx1]!=last)
156+
last=snap->xip[idx2++]=snap->xip[idx1];
157+
else
158+
snap->nxip--;
159+
idx1++;
160+
}
161+
}
144162
}
145163

146164
/*
@@ -295,10 +313,12 @@ parse_snapshot(const char *str)
295313
str=endp;
296314

297315
/* require the input to be in order */
298-
if (val<xmin||val >=xmax||val <=last_val)
316+
if (val<xmin||val >=xmax||val<last_val)
299317
gotobad_format;
300318

301-
buf_add_txid(buf,val);
319+
/* skip duplicates */
320+
if (val!=last_val)
321+
buf_add_txid(buf,val);
302322
last_val=val;
303323

304324
if (*str==',')
@@ -361,8 +381,7 @@ txid_current_snapshot(PG_FUNCTION_ARGS)
361381
{
362382
TxidSnapshot*snap;
363383
uint32nxip,
364-
i,
365-
size;
384+
i;
366385
TxidEpochstate;
367386
Snapshotcur;
368387

@@ -381,9 +400,7 @@ txid_current_snapshot(PG_FUNCTION_ARGS)
381400

382401
/* allocate */
383402
nxip=cur->xcnt;
384-
size=TXID_SNAPSHOT_SIZE(nxip);
385-
snap=palloc(size);
386-
SET_VARSIZE(snap,size);
403+
snap=palloc(TXID_SNAPSHOT_SIZE(nxip));
387404

388405
/* fill */
389406
snap->xmin=convert_xid(cur->xmin,&state);
@@ -392,9 +409,18 @@ txid_current_snapshot(PG_FUNCTION_ARGS)
392409
for (i=0;i<nxip;i++)
393410
snap->xip[i]=convert_xid(cur->xip[i],&state);
394411

395-
/* we want them guaranteed to be in ascending order */
412+
/*
413+
* We want them guaranteed to be in ascending order. This also removes
414+
* any duplicate xids. Normally, an XID can only be assigned to one
415+
* backend, but when preparing a transaction for two-phase commit, there
416+
* is a transient state when both the original backend and the dummy
417+
* PGPROC entry reserved for the prepared transaction hold the same XID.
418+
*/
396419
sort_snapshot(snap);
397420

421+
/* set size after sorting, because it may have removed duplicate xips */
422+
SET_VARSIZE(snap,TXID_SNAPSHOT_SIZE(snap->nxip));
423+
398424
PG_RETURN_POINTER(snap);
399425
}
400426

@@ -472,18 +498,27 @@ txid_snapshot_recv(PG_FUNCTION_ARGS)
472498
snap=palloc(TXID_SNAPSHOT_SIZE(nxip));
473499
snap->xmin=xmin;
474500
snap->xmax=xmax;
475-
snap->nxip=nxip;
476-
SET_VARSIZE(snap,TXID_SNAPSHOT_SIZE(nxip));
477501

478502
for (i=0;i<nxip;i++)
479503
{
480504
txidcur=pq_getmsgint64(buf);
481505

482-
if (cur <=last||cur<xmin||cur >=xmax)
506+
if (cur<last||cur<xmin||cur >=xmax)
483507
gotobad_format;
508+
509+
/* skip duplicate xips */
510+
if (cur==last)
511+
{
512+
i--;
513+
nxip--;
514+
continue;
515+
}
516+
484517
snap->xip[i]=cur;
485518
last=cur;
486519
}
520+
snap->nxip=nxip;
521+
SET_VARSIZE(snap,TXID_SNAPSHOT_SIZE(nxip));
487522
PG_RETURN_POINTER(snap);
488523

489524
bad_format:

‎src/test/regress/expected/txid.out

Lines changed: 6 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -12,6 +12,12 @@ select '12:18:14,16'::txid_snapshot;
1212
12:18:14,16
1313
(1 row)
1414

15+
select '12:16:14,14'::txid_snapshot;
16+
txid_snapshot
17+
---------------
18+
12:16:14
19+
(1 row)
20+
1521
-- errors
1622
select '31:12:'::txid_snapshot;
1723
ERROR: invalid input for txid_snapshot: "31:12:"
@@ -29,10 +35,6 @@ select '12:16:14,13'::txid_snapshot;
2935
ERROR: invalid input for txid_snapshot: "12:16:14,13"
3036
LINE 1: select '12:16:14,13'::txid_snapshot;
3137
^
32-
select '12:16:14,14'::txid_snapshot;
33-
ERROR: invalid input for txid_snapshot: "12:16:14,14"
34-
LINE 1: select '12:16:14,14'::txid_snapshot;
35-
^
3638
create temp table snapshot_test (
3739
nrinteger,
3840
snaptxid_snapshot

‎src/test/regress/sql/txid.sql

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3,13 +3,13 @@
33
-- i/o
44
select'12:13:'::txid_snapshot;
55
select'12:18:14,16'::txid_snapshot;
6+
select'12:16:14,14'::txid_snapshot;
67

78
-- errors
89
select'31:12:'::txid_snapshot;
910
select'0:1:'::txid_snapshot;
1011
select'12:13:0'::txid_snapshot;
1112
select'12:16:14,13'::txid_snapshot;
12-
select'12:16:14,14'::txid_snapshot;
1313

1414
create temp table snapshot_test (
1515
nrinteger,

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