[clue] postgres questions?
beandaemon at gmail.com
Mon Dec 5 13:41:49 MST 2016
It's 8.4 - unfortunately we're having some problems with
autovacum appearing to be configured correctly, not realistically running
when it should
POSTGRES_LAST_AUTOVACUUM CRITICAL: DB "xe" (host:localhost) (port=1935) DB:
xe TABLE: pg_catalog.pg_class: 17:11 November 18, 2016 (16 days 20 hours 23
the thursday log is largely full of checkpoint_segments spam, and ONE
DETAIL: Process 9758 waits for ShareLock on transaction 40741339; blocked
by process 9794.
Process 9794 waits for ShareLock on transaction 40740891; blocked
by process 9758.
Process 9758: select * from rhn_channel.update_needed_cache($1) as
there hasn't been much in the way of logging since the deadlock, just more
HINT: Consider increasing the configuration parameter
LOG: checkpoints are occurring too frequently (16 seconds apart)
Since as near as I can tell the only meaningful logging over the last 4
days is the deadlock, I'm inclined to think the deadlock has some
relationship with the DB growing 40GB over the weekend. Quentin's
probably right, I probably need to turn up the logging levels. Do we know
where those are? in the .conf file?
On Mon, Dec 5, 2016 at 11:06 AM, Grant Johnson <grant at amadensor.com> wrote:
> There is a good chance that the Thursday log holds some clues about what
> the activity was. It is likely repeated often, and will be easy to
> find, as it was happening a lot. If the volume was very high, you also
> see messages about checkpoints, because changes were out pacing the
> normal background DB writes. If these were happening only during this
> anomalous time, I would not worry about it, but if it happens during
> normal operations, some tuning changes may be needed.
> If you are having updates that exceed your free space map, the normal
> vacuum will not release the space, and instead you will need to run a
> vacuum full, which has the unfortunate side effect of locking tables
> while it runs, so it impedes write operations.
> So, I would look at the log, see if anything starts making sense, and
> then clean up with a full vacuum during a low activity time, and perhaps
> a reindex all. I have found that doing full clean up every year or so
> helps, but generally, leaving the free space in the files with normal
> vacuum/auto-vacuum helps performance.
> On Mon, 2016-12-05 at 07:47 -0700, Mike Bean wrote:
> > Of particular interest is
> > -rw------- 1 postgres postgres 94479 Dec 2 21:29 postgresql-Fri.log
> > -rw------- 1 postgres postgres 0 Dec 5 00:00 postgresql-Mon.log
> > -rw------- 1 postgres postgres 0 Dec 3 00:00 postgresql-Sat.log
> > -rw------- 1 postgres postgres 0 Dec 4 00:00 postgresql-Sun.log
> > -rw------- 1 postgres postgres 208184 Dec 1 23:59 postgresql-Thu.log
> > -rw------- 1 postgres postgres 86154 Nov 29 21:57 postgresql-Tue.log
> > -rw------- 1 postgres postgres 89399 Nov 30 21:48 postgresql-Wed.log
> > Huh - want to bet the writes were actually on thursday? The plot
> > thickens!
> > On Mon, Dec 5, 2016 at 7:43 AM, Mike Bean <beandaemon at gmail.com>
> > wrote:
> > Do we have members who are comfortable/skilled with postgres?
> > Long story short we have a spacewalk server running
> > postgres and the DB is showing really erratic behavior. We
> > used to do weekly vacuums to keep it from running out of
> > space, I figured out that doing a reindex bumped the free
> > space from 20-80 GB. Over the weekend, it dropped to roughly
> > 60, we went one week without doing a vacuum reindex, and it's
> > back down to 20.
> > I know for a fact there's no one else in the organization
> > making major changes on this DB, and certainly nothing that
> > could justify 40GB of writes in 3 days. Not really being a
> > DBA, I'm running low on my bag of tricks, thought I'd see if
> > CLUE had any advice. Running vacuums once a week to keep it
> > from filling the disk feels like taking aspirin to get over
> > your gunshot wound. Sure, it'll keep the server running, but
> > ultimately what I really want to know is why a largely static
> > spacewalk DB is writing 60GB to the disk in a 2 week interval.
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