diff options
| author | Alvaro Herrera <alvherre@alvh.no-ip.org> | 2017-01-19 18:23:09 -0300 |
|---|---|---|
| committer | Alvaro Herrera <alvherre@alvh.no-ip.org> | 2017-01-19 18:24:17 -0300 |
| commit | 8eace46d34ab6ac0d887aa4d3504bc4222c2e448 (patch) | |
| tree | 1e6d8a76c81c56b452eff3885381f7d998aee7f7 /src/include/access/xlog_internal.h | |
| parent | 8b0fec93ecc788c8d8b329d41ab795712d8dcc5a (diff) | |
Fix race condition in reading commit timestamps
If a user requests the commit timestamp for a transaction old enough
that its data is concurrently being truncated away by vacuum at just the
right time, they would receive an ugly internal file-not-found error
message from slru.c rather than the expected NULL return value.
In a primary server, the window for the race is very small: the lookup
has to occur exactly between the two calls by vacuum, and there's not a
lot that happens between them (mostly just a multixact truncate). In a
standby server, however, the window is larger because the truncation is
executed as soon as the WAL record for it is replayed, but the advance
of the oldest-Xid is not executed until the next checkpoint record.
To fix in the primary, simply reverse the order of operations in
vac_truncate_clog. To fix in the standby, augment the WAL truncation
record so that the standby is aware of the new oldest-XID value and can
apply the update immediately. WAL version bumped because of this.
No backpatch, because of the low importance of the bug and its rarity.
Author: Craig Ringer
Reviewed-By: Petr Jelínek, Peter Eisentraut
Discussion: https://postgr.es/m/CAMsr+YFhVtRQT1VAwC+WGbbxZZRzNou=N9Ed-FrCqkwQ8H8oJQ@mail.gmail.com
Diffstat (limited to 'src/include/access/xlog_internal.h')
| -rw-r--r-- | src/include/access/xlog_internal.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index e0fcd056776..8ad4d47d127 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -31,7 +31,7 @@ /* * Each page of XLOG file has a header like this: */ -#define XLOG_PAGE_MAGIC 0xD093 /* can be used as WAL version indicator */ +#define XLOG_PAGE_MAGIC 0xD094 /* can be used as WAL version indicator */ typedef struct XLogPageHeaderData { |