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Commitc89a0dd

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Repair longstanding bug in slru/clog logic: it is possible for two backends
to try to create a log segment file concurrently, but the code erroneouslyspecified O_EXCL to open(), resulting in a needless failure. Before 7.4,it was even a PANIC condition :-(. Correct code is actually simpler thanwhat we had, because we can just say O_CREAT to start with and not need asecond open() call. I believe this accounts for several recent reports ofhard-to-reproduce "could not create file ...: File exists" errors in bothpg_clog and pg_subtrans.
1 parent4789e98 commitc89a0dd

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1 file changed

+10
-25
lines changed
  • src/backend/access/transam

1 file changed

+10
-25
lines changed

‎src/backend/access/transam/slru.c‎

Lines changed: 10 additions & 25 deletions
Original file line numberDiff line numberDiff line change
@@ -41,7 +41,7 @@
4141
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
4242
* Portions Copyright (c) 1994, Regents of the University of California
4343
*
44-
* $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.33 2005/12/06 23:08:32 tgl Exp $
44+
* $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.34 2006/01/21 04:38:21 tgl Exp $
4545
*
4646
*-------------------------------------------------------------------------
4747
*/
@@ -128,7 +128,6 @@ typedef struct SlruFlushData
128128
typedefenum
129129
{
130130
SLRU_OPEN_FAILED,
131-
SLRU_CREATE_FAILED,
132131
SLRU_SEEK_FAILED,
133132
SLRU_READ_FAILED,
134133
SLRU_WRITE_FAILED,
@@ -652,26 +651,19 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruFlush fdata)
652651
* transactions that have already been truncated from the commit log.
653652
* Easiest way to deal with that is to accept references to
654653
* nonexistent files here and in SlruPhysicalReadPage.)
654+
*
655+
* Note: it is possible for more than one backend to be executing
656+
* this code simultaneously for different pages of the same file.
657+
* Hence, don't use O_EXCL or O_TRUNC or anything like that.
655658
*/
656659
SlruFileName(ctl,path,segno);
657-
fd=BasicOpenFile(path,O_RDWR |PG_BINARY,S_IRUSR |S_IWUSR);
660+
fd=BasicOpenFile(path,O_RDWR |O_CREAT |PG_BINARY,
661+
S_IRUSR |S_IWUSR);
658662
if (fd<0)
659663
{
660-
if (errno!=ENOENT)
661-
{
662-
slru_errcause=SLRU_OPEN_FAILED;
663-
slru_errno=errno;
664-
return false;
665-
}
666-
667-
fd=BasicOpenFile(path,O_RDWR |O_CREAT |O_EXCL |PG_BINARY,
668-
S_IRUSR |S_IWUSR);
669-
if (fd<0)
670-
{
671-
slru_errcause=SLRU_CREATE_FAILED;
672-
slru_errno=errno;
673-
return false;
674-
}
664+
slru_errcause=SLRU_OPEN_FAILED;
665+
slru_errno=errno;
666+
return false;
675667
}
676668

677669
if (fdata)
@@ -763,13 +755,6 @@ SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid)
763755
errdetail("could not open file \"%s\": %m",
764756
path)));
765757
break;
766-
caseSLRU_CREATE_FAILED:
767-
ereport(ERROR,
768-
(errcode_for_file_access(),
769-
errmsg("could not access status of transaction %u",xid),
770-
errdetail("could not create file \"%s\": %m",
771-
path)));
772-
break;
773758
caseSLRU_SEEK_FAILED:
774759
ereport(ERROR,
775760
(errcode_for_file_access(),

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