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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 04:38:46 +00:00
parent e05a95bc00
commit 7da4e7ac6a
1 changed files with 10 additions and 25 deletions
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29
src/backend/access/transam/slru.c
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@ -6,7 +6,7 @@
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* $Header: /cvsroot/pgsql/src/backend/access/transam/slru.c,v 1.7.2.2 2005/11/03 00:23:50 tgl Exp $ * $Header: /cvsroot/pgsql/src/backend/access/transam/slru.c,v 1.7.2.3 2006/01/21 04:38:46 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -133,7 +133,6 @@ typedef SlruSharedData *SlruShared;
typedef enum typedef enum
{ {
SLRU_OPEN_FAILED, SLRU_OPEN_FAILED,
SLRU_CREATE_FAILED,
SLRU_SEEK_FAILED, SLRU_SEEK_FAILED,
SLRU_READ_FAILED, SLRU_READ_FAILED,
SLRU_WRITE_FAILED SLRU_WRITE_FAILED
@ -554,27 +553,20 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno)
* transactions that have already been truncated from the commit log. * transactions that have already been truncated from the commit log.
* Easiest way to deal with that is to accept references to * Easiest way to deal with that is to accept references to
* nonexistent files here and in SlruPhysicalReadPage.) * nonexistent files here and in SlruPhysicalReadPage.)
*
* 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 (fd < 0)
{
if (errno != ENOENT)
{ {
slru_errcause = SLRU_OPEN_FAILED; slru_errcause = SLRU_OPEN_FAILED;
slru_errno = errno; slru_errno = errno;
return false; return false;
} }
fd = BasicOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
S_IRUSR | S_IWUSR);
if (fd < 0)
{
slru_errcause = SLRU_CREATE_FAILED;
slru_errno = errno;
return false;
}
}
if (lseek(fd, (off_t) offset, SEEK_SET) < 0) if (lseek(fd, (off_t) offset, SEEK_SET) < 0)
{ {
slru_errcause = SLRU_SEEK_FAILED; slru_errcause = SLRU_SEEK_FAILED;
@ -620,13 +612,6 @@ SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid)
errdetail("could not open file \"%s\": %m", errdetail("could not open file \"%s\": %m",
path))); path)));
break; break;
case SLRU_CREATE_FAILED:
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not access status of transaction %u", xid),
errdetail("could not create file \"%s\": %m",
path)));
break;
case SLRU_SEEK_FAILED: case SLRU_SEEK_FAILED:
ereport(ERROR, ereport(ERROR,
(errcode_for_file_access(), (errcode_for_file_access(),