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Commitdb18703

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committed
Fix LISTEN/NOTIFY race condition reported by Gavin Sherry. While a
really general fix might be difficult, I believe the only case whereAtCommit_Notify could see an uncommitted tuple is where the other guyhas just unlistened and not yet committed. The best solution seems tobe to just skip updating that tuple, on the assumption that the otherguy does not want to hear about the notification anyway. This is notperfect --- if the other guy rolls back his unlisten instead of committing,then he really should have gotten this notify. But to do that, we'd haveto wait to see if he commits or not, or make UNLISTEN hold exclusive lockon pg_listener until commit. Either of these answers is deadlock-prone,not to mention horrible for interactive performance. Do it this wayfor now. (What happened to that project to do LISTEN/NOTIFY in memorywith no table, anyway?)
1 parentd73e1b3 commitdb18703

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4 files changed

+92
-19
lines changed

4 files changed

+92
-19
lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 29 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/access/heap/heapam.c,v 1.154 2003/08/04 02:39:57 momjian Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/heap/heapam.c,v 1.155 2003/09/15 23:33:38 tgl Exp $
1212
*
1313
*
1414
* INTERFACE ROUTINES
@@ -1206,10 +1206,15 @@ simple_heap_insert(Relation relation, HeapTuple tup)
12061206
*
12071207
* NB: do not call this directly unless you are prepared to deal with
12081208
* concurrent-update conditions. Use simple_heap_delete instead.
1209+
*
1210+
* Normal, successful return value is HeapTupleMayBeUpdated, which
1211+
* actually means we did delete it. Failure return codes are
1212+
* HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
1213+
* (the last only possible if wait == false).
12091214
*/
12101215
int
12111216
heap_delete(Relationrelation,ItemPointertid,
1212-
ItemPointerctid,CommandIdcid)
1217+
ItemPointerctid,CommandIdcid,boolwait)
12131218
{
12141219
ItemIdlp;
12151220
HeapTupleDatatp;
@@ -1243,7 +1248,7 @@ heap_delete(Relation relation, ItemPointer tid,
12431248
ReleaseBuffer(buffer);
12441249
elog(ERROR,"attempted to delete invisible tuple");
12451250
}
1246-
elseif (result==HeapTupleBeingUpdated)
1251+
elseif (result==HeapTupleBeingUpdated&&wait)
12471252
{
12481253
TransactionIdxwait=HeapTupleHeaderGetXmax(tp.t_data);
12491254

@@ -1275,7 +1280,9 @@ heap_delete(Relation relation, ItemPointer tid,
12751280
}
12761281
if (result!=HeapTupleMayBeUpdated)
12771282
{
1278-
Assert(result==HeapTupleSelfUpdated||result==HeapTupleUpdated);
1283+
Assert(result==HeapTupleSelfUpdated||
1284+
result==HeapTupleUpdated||
1285+
result==HeapTupleBeingUpdated);
12791286
*ctid=tp.t_data->t_ctid;
12801287
LockBuffer(buffer,BUFFER_LOCK_UNLOCK);
12811288
ReleaseBuffer(buffer);
@@ -1369,7 +1376,10 @@ simple_heap_delete(Relation relation, ItemPointer tid)
13691376
ItemPointerDatactid;
13701377
intresult;
13711378

1372-
result=heap_delete(relation,tid,&ctid,GetCurrentCommandId());
1379+
result=heap_delete(relation,tid,
1380+
&ctid,
1381+
GetCurrentCommandId(),
1382+
true/* wait for commit */);
13731383
switch (result)
13741384
{
13751385
caseHeapTupleSelfUpdated:
@@ -1396,10 +1406,15 @@ simple_heap_delete(Relation relation, ItemPointer tid)
13961406
*
13971407
* NB: do not call this directly unless you are prepared to deal with
13981408
* concurrent-update conditions. Use simple_heap_update instead.
1409+
*
1410+
* Normal, successful return value is HeapTupleMayBeUpdated, which
1411+
* actually means we *did* update it. Failure return codes are
1412+
* HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
1413+
* (the last only possible if wait == false).
13991414
*/
14001415
int
14011416
heap_update(Relationrelation,ItemPointerotid,HeapTuplenewtup,
1402-
ItemPointerctid,CommandIdcid)
1417+
ItemPointerctid,CommandIdcid,boolwait)
14031418
{
14041419
ItemIdlp;
14051420
HeapTupleDataoldtup;
@@ -1443,7 +1458,7 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
14431458
ReleaseBuffer(buffer);
14441459
elog(ERROR,"attempted to update invisible tuple");
14451460
}
1446-
elseif (result==HeapTupleBeingUpdated)
1461+
elseif (result==HeapTupleBeingUpdated&&wait)
14471462
{
14481463
TransactionIdxwait=HeapTupleHeaderGetXmax(oldtup.t_data);
14491464

@@ -1475,7 +1490,9 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
14751490
}
14761491
if (result!=HeapTupleMayBeUpdated)
14771492
{
1478-
Assert(result==HeapTupleSelfUpdated||result==HeapTupleUpdated);
1493+
Assert(result==HeapTupleSelfUpdated||
1494+
result==HeapTupleUpdated||
1495+
result==HeapTupleBeingUpdated);
14791496
*ctid=oldtup.t_data->t_ctid;
14801497
LockBuffer(buffer,BUFFER_LOCK_UNLOCK);
14811498
ReleaseBuffer(buffer);
@@ -1699,7 +1716,10 @@ simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
16991716
ItemPointerDatactid;
17001717
intresult;
17011718

1702-
result=heap_update(relation,otid,tup,&ctid,GetCurrentCommandId());
1719+
result=heap_update(relation,otid,tup,
1720+
&ctid,
1721+
GetCurrentCommandId(),
1722+
true/* wait for commit */);
17031723
switch (result)
17041724
{
17051725
caseHeapTupleSelfUpdated:

‎src/backend/commands/async.c

Lines changed: 55 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1994, Regents of the University of California
88
*
99
* IDENTIFICATION
10-
* $Header: /cvsroot/pgsql/src/backend/commands/async.c,v 1.99 2003/09/1500:26:31 petere Exp $
10+
* $Header: /cvsroot/pgsql/src/backend/commands/async.c,v 1.100 2003/09/1523:33:39 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -515,13 +515,58 @@ AtCommit_Notify(void)
515515
}
516516
elseif (listener->notification==0)
517517
{
518+
ItemPointerDatactid;
519+
intresult;
520+
518521
rTuple=heap_modifytuple(lTuple,lRel,
519522
value,nulls,repl);
520-
simple_heap_update(lRel,&lTuple->t_self,rTuple);
523+
/*
524+
* We cannot use simple_heap_update here because the tuple
525+
* could have been modified by an uncommitted transaction;
526+
* specifically, since UNLISTEN releases exclusive lock on
527+
* the table before commit, the other guy could already have
528+
* tried to unlisten. There are no other cases where we
529+
* should be able to see an uncommitted update or delete.
530+
* Therefore, our response to a HeapTupleBeingUpdated result
531+
* is just to ignore it. We do *not* wait for the other
532+
* guy to commit --- that would risk deadlock, and we don't
533+
* want to block while holding the table lock anyway for
534+
* performance reasons. We also ignore HeapTupleUpdated,
535+
* which could occur if the other guy commits between our
536+
* heap_getnext and heap_update calls.
537+
*/
538+
result=heap_update(lRel,&lTuple->t_self,rTuple,
539+
&ctid,
540+
GetCurrentCommandId(),
541+
false/* no wait for commit */);
542+
switch (result)
543+
{
544+
caseHeapTupleSelfUpdated:
545+
/* Tuple was already updated in current command? */
546+
elog(ERROR,"tuple already updated by self");
547+
break;
548+
549+
caseHeapTupleMayBeUpdated:
550+
/* done successfully */
521551

522552
#ifdefNOT_USED/* currently there are no indexes */
523-
CatalogUpdateIndexes(lRel,rTuple);
553+
CatalogUpdateIndexes(lRel,rTuple);
524554
#endif
555+
break;
556+
557+
caseHeapTupleBeingUpdated:
558+
/* ignore uncommitted tuples */
559+
break;
560+
561+
caseHeapTupleUpdated:
562+
/* ignore just-committed tuples */
563+
break;
564+
565+
default:
566+
elog(ERROR,"unrecognized heap_update status: %u",
567+
result);
568+
break;
569+
}
525570
}
526571
}
527572
}
@@ -803,7 +848,13 @@ ProcessIncomingNotify(void)
803848
relname, (int)sourcePID);
804849

805850
NotifyMyFrontEnd(relname,sourcePID);
806-
/* Rewrite the tuple with 0 in notification column */
851+
/*
852+
* Rewrite the tuple with 0 in notification column.
853+
*
854+
* simple_heap_update is safe here because no one else would
855+
* have tried to UNLISTEN us, so there can be no uncommitted
856+
* changes.
857+
*/
807858
rTuple=heap_modifytuple(lTuple,lRel,value,nulls,repl);
808859
simple_heap_update(lRel,&lTuple->t_self,rTuple);
809860

‎src/backend/executor/execMain.c

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -26,7 +26,7 @@
2626
*
2727
*
2828
* IDENTIFICATION
29-
* $Header: /cvsroot/pgsql/src/backend/executor/execMain.c,v 1.216 2003/08/08 21:41:34 momjian Exp $
29+
* $Header: /cvsroot/pgsql/src/backend/executor/execMain.c,v 1.217 2003/09/15 23:33:43 tgl Exp $
3030
*
3131
*-------------------------------------------------------------------------
3232
*/
@@ -1406,7 +1406,8 @@ ExecDelete(TupleTableSlot *slot,
14061406
ldelete:;
14071407
result=heap_delete(resultRelationDesc,tupleid,
14081408
&ctid,
1409-
estate->es_snapshot->curcid);
1409+
estate->es_snapshot->curcid,
1410+
true/* wait for commit */);
14101411
switch (result)
14111412
{
14121413
caseHeapTupleSelfUpdated:
@@ -1540,7 +1541,8 @@ lreplace:;
15401541
*/
15411542
result=heap_update(resultRelationDesc,tupleid,tuple,
15421543
&ctid,
1543-
estate->es_snapshot->curcid);
1544+
estate->es_snapshot->curcid,
1545+
true/* wait for commit */);
15441546
switch (result)
15451547
{
15461548
caseHeapTupleSelfUpdated:

‎src/include/access/heapam.h

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $Id: heapam.h,v 1.83 2003/08/04 02:40:10 momjian Exp $
10+
* $Id: heapam.h,v 1.84 2003/09/15 23:33:43 tgl Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -155,9 +155,9 @@ extern void setLastTid(const ItemPointer tid);
155155

156156
externOidheap_insert(Relationrelation,HeapTupletup,CommandIdcid);
157157
externintheap_delete(Relationrelation,ItemPointertid,ItemPointerctid,
158-
CommandIdcid);
158+
CommandIdcid,boolwait);
159159
externintheap_update(Relationrelation,ItemPointerotid,HeapTupletup,
160-
ItemPointerctid,CommandIdcid);
160+
ItemPointerctid,CommandIdcid,boolwait);
161161
externintheap_mark4update(Relationrelation,HeapTupletup,
162162
Buffer*userbuf,CommandIdcid);
163163

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