From c89a0dd3bb2c1ab5d375335fee1af523e73f79cb Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 21 Jan 2006 04:38:21 +0000
Subject: [PATCH] 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 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.
---
src/backend/access/transam/slru.c | 35 +++++++++----------------------
1 file changed, 10 insertions(+), 25 deletions(-)
diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index d1bfd9570c..2079d08b1e 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -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,
@@ -652,26 +651,19 @@ 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;
- }
+ slru_errcause = SLRU_OPEN_FAILED;
+ slru_errno = errno;
+ return false;
}
if (fdata)
@@ -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(),