On Sat, Oct 17, 2015 at 5:30 AM, <
l@lrowe.co.uk> wrote:
> I'm seeing Postgres 9.4.5 archive while idle every archive_timeout when I
> set ``wal_level hot_standby``.
> At ``wal_level archive`` I only see archiving every checkpoint_timeout (that
> it archives every checkpoint_timeout is a known limitation, see
>
http://www.postgresql.org/message-id/1407389876762-5813999.post@n5.nabble.com):
> I think this additional archiving at wal_level hot_standby is a bug.
Agreed. There is indeed a difference between the way 9.3 and 9.4 behave. When wal_level = hot_standby, with 9.4 a segment will be archived depending on archive_timeout as you mention, and that's not the case of 9.3. There is definitely a regression here: we should not archive a segment if there is no activity.
If I look at the contents of the segments with 9.4 when there is no activity, I am seeing that actually a record XLOG_RUNNING_XACTS is generated all the time after switching a segment, leading to the archiving of this segment because server thinks that there is new data, and actually there is, so the segment will be archived... Here is for example the output of pg_xlogdump in this case:
$ pg_xlogdump 000000010000000000000018
rmgr: Standby len (rec/tot): 24/ 56, tx: 0, lsn: 0/18000028, prev 0/17000060, bkp: 0000, desc: running xacts: nextXid 1001 latestCompletedXid 1000 oldestRunningXid 1001
rmgr: XLOG len (rec/tot): 0/ 32, tx: 0, lsn: 0/18000060, prev 0/18000028, bkp: 0000, desc: xlog switch
