Thanks for the notes and the useful page link on "vacuum full". We are running "vacuum full" primarily because a number of tables in our database have a very large amount of data added to them during each day, all of which is deleted in one large series of "delete from" statements early in the morning before we perform the vacuum. Comments like the one here (http://www.postgresql.org/docs/9.0/static/routine-vacuuming.html) led us to think that with this type of situation (very large deletes daily) autovacuum would not in the end be sufficient over the long run.
That said, it sounds like if we switched to daily "trucates" of each table (they can be purged entirely each day) rather than "delete froms", then there truly would not be any reason to use "vacuum full". Does that sound plausible?
Thanks again,
Daniel
On Thu, Jul 7, 2011 at 5:30 PM, Greg Smith <greg@xxxxxxxxxxxxxxx> wrote:
On 07/07/2011 04:30 PM, D C wrote:These are slightly strange settings. How did you come up with them? The autovacuum_vacuum_scale_factor being so high is particularly dangerous. If anything, you should be reducing that from its default of 0.2, not increasing it further.
autovacuum_naptime = 30s
autovacuum_vacuum_threshold = 200
autovacuum_vacuum_scale_factor = 0.5
autovacuum_vacuum_cost_delay = 10
VACUUM FULL takes an exclusive lock on the table while it runs, and it extremely problematic for several other reasons too. See http://wiki.postgresql.org/wiki/VACUUM_FULL for more information.
In addition to autovacuuming, each day, early, in the morning, we run a full vacuum, like this: "vacuumdb --all --full --analyze". We do not have any special variable set for vacuum in postgresql.conf.
You didn't mention your PostgreSQL version so I can't be sure exactly how bad of a problem you're causing with this, but you should almost certainly stop doing it.Yes. VACUUM FULL needs to take a large lock on the table, and it will kick out autovacuum in that case, and cause countless other trouble too. And if the VACUUM FULL is already running, other things will end up getting stuck waiting for it, and all sorts of locking issues can come out of that.
The problem is that once or twice a week, the "vacuum full analyze" seems to cancel out the autovacuum that has already started at the same time. E.g.,
You should remove the "--full" from your daily routine, reduce autovacuum_vacuum_scale_factor back to a reasonable number again, and see how things go after that. You're trying to use PostgreSQL in a way it's known not to work well right now.The cost limit has nothing to do with the issue you're seeing. It adjust how much work autovacuum does at any moment in time, it isn't involved in any prioritization.
I am guessing that we can do the above by setting the "autovacuum_vacuum_cost_limit" to a fairly high value (rather than it not being set at all, as it is right now, and thus inheriting the "200" default value from vacuum_cost_limit).
--
Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD
Comprehensive and Customized PostgreSQL Training Classes:
http://www.2ndquadrant.us/postgresql-training/
--
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance
