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authorTom Lane2006-01-21 04:38:54 +0000
committerTom Lane2006-01-21 04:38:54 +0000
commit3cbc8b6fb483ae4bf3011abe49030cb057a2722b (patch)
treeb41630ece8bea8f65a3e2990fcf0e28bf5c8430f
parenta6cc7db9a67663d59ceb6328d2b0ccea7b384ef6 (diff)
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.
-rw-r--r--src/backend/access/transam/clog.c18
1 files changed, 8 insertions, 10 deletions
diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c
index 3f50c79331b..dca6b70dacc 100644
--- a/src/backend/access/transam/clog.c
+++ b/src/backend/access/transam/clog.c
@@ -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",