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Repair longstanding bug in slru/clog logic: it is possible for two backends

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to try to create a log segment file concurrently, but the code erroneously
specified O_EXCL to open(), resulting in a needless failure.  Before 7.4,
it was even a PANIC condition :-(.  Correct code is actually simpler than
what we had, because we can just say O_CREAT to start with and not need a
second open() call.  I believe this accounts for several recent reports of
hard-to-reproduce "could not create file ...: File exists" errors in both
pg_clog and pg_subtrans.
This commit is contained in:
Tom Lane 2006-01-21 04:38:54 +00:00
parent a6cc7db9a6
commit 3cbc8b6fb4
1 changed files with 8 additions and 10 deletions
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18
src/backend/access/transam/clog.c
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@ -13,7 +13,7 @@
* Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $Header: /cvsroot/pgsql/src/backend/access/transam/clog.c,v 1.11.2.1 2005/11/03 00:23:57 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/access/transam/clog.c,v 1.11.2.2 2006/01/21 04:38:54 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -598,17 +598,15 @@ CLOGPhysicalWritePage(int pageno, int slotno)
* that have already been truncated from the commit log. Easiest way
* to deal with that is to accept references to nonexistent files here
* and in CLOGPhysicalReadPage.)
*
* Note: it is possible for more than one backend to be executing
* this code simultaneously for different pages of the same file.
* Hence, don't use O_EXCL or O_TRUNC or anything like that.
*/
fd = BasicOpenFile(path, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR);
fd = BasicOpenFile(path, O_RDWR | O_CREAT | PG_BINARY,
S_IRUSR | S_IWUSR);
if (fd < 0)
{
if (errno != ENOENT)
elog(PANIC, "open of %s failed: %m", path);
fd = BasicOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
S_IRUSR | S_IWUSR);
if (fd < 0)
elog(PANIC, "creation of file %s failed: %m", path);
}
elog(PANIC, "open of %s failed: %m", path);
if (lseek(fd, (off_t) offset, SEEK_SET) < 0)
elog(PANIC, "lseek of clog file %u, offset %u failed: %m",