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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 04:38:21 +00:00
parent 4789e98801
commit c89a0dd3bb
1 changed files with 10 additions and 25 deletions
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29
src/backend/access/transam/slru.c
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@ -41,7 +41,7 @@
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.33 2005/12/06 23:08:32 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.34 2006/01/21 04:38:21 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -128,7 +128,6 @@ typedef struct SlruFlushData
typedef enum
{
SLRU_OPEN_FAILED,
SLRU_CREATE_FAILED,
SLRU_SEEK_FAILED,
SLRU_READ_FAILED,
SLRU_WRITE_FAILED,
@ -652,28 +651,21 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruFlush fdata)
* transactions 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 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.
*/
SlruFileName(ctl, path, segno);
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)
{
slru_errcause = SLRU_OPEN_FAILED;
slru_errno = errno;
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 (fdata)
{
if (fdata->num_files < MAX_FLUSH_BUFFERS)
@ -763,13 +755,6 @@ SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid)
errdetail("could not open file \"%s\": %m",
path)));
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:
ereport(ERROR,
(errcode_for_file_access(),