[PERFORM] "VACUUM FULL ANALYZE" vs. Autovacuum Contention
Hello, (Apologies for any possible duplication of this email.) (Also, apologies if this is an obvious question. I have gone through the archives without seeing something that directly ties to this.) We are running Postgresql on a 64b RHEL5.2 64b server. "Uname -a": --Linux xxx 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:15 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux We have autovacuum enabled with the following settings: autovacuum_naptime = 30s autovacuum_vacuum_threshold = 200 autovacuum_vacuum_scale_factor = 0.5 autovacuum_vacuum_cost_delay = 10 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. 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., -2011-05-07 03:51:04.959 EDT--[unknown]-[unknown] [3348]LOG: connection received: host=##.##.##.## port=60470 -2011-05-07 03:51:04.959 EDT-##.##.##.##-- [3348]LOG: connection authorized: user= database= -2011-05-07 03:51:04.961 EDT-##.##.##.##-- [3348]LOG: statement: VACUUM FULL ANALYZE; -... -2011-05-07 03:51:10.733 EDT--- [19879]ERROR: canceling autovacuum task -2011-05-07 03:51:10.733 EDT--- [19879]CONTEXT: automatic vacuum of table ".xxx." -... -2011-05-07 03:52:48.918 EDT-##.##.##.##-- [3348]LOG: duration: 103957.270 ms -2011-05-07 03:52:48.920 EDT-##.##.##.##-- [3348]LOG: disconnection: session time: 0:01:43.961 user= database= host=##.##.##.## port=60470 We would like to eliminate this error. A bigger problem is that sometimes it seems like autovacuum wins out over "vacuum full analyze". This tends to result in a hung job on our client, with other ensuing complications. * Our basic question is what method we might be able to use to prevent either of these jobs from canceling. What we would like is, instead of autovacuum canceling, it rather always defers to "vacuum full analyze" job, waiting for it to complete. 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). Does that sound right? (If, what might be a good value to set?) Or perhaps there is a more foolproof way of doing this that does not rely upon guesswork? Any suggestions at all would be most welcome! Daniel C.
Re: [PERFORM] "VACUUM FULL ANALYZE" vs. Autovacuum Contention
That's a great point about autovacuum_vacuum_scale_factor; I will lower the value there to 0.2 and see if autovacuum starts doing a better job. (We use Postgresql 8.3.5 currently, by the way.) 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 wrote: > On 07/07/2011 04:30 PM, D C wrote: > >> >> autovacuum_naptime = 30s >> autovacuum_vacuum_threshold = 200 >> autovacuum_vacuum_scale_factor = 0.5 >> autovacuum_vacuum_cost_delay = 10 >> >> > 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. > > > 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. >> >> > 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<http://wiki.postgresql.org/wiki/VACUUM_FULL>for > more information. > > 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. > > > > 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., >> >> > 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. > > 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. > > > 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). >> >> > 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. > > -- > Greg Smith 2ndQuadrant USg...@2ndquadrant.com Baltimore, MD > Comprehensive and Customized PostgreSQL Training Classes: > http://www.2ndquadrant.us/**postgresql-training/<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<http://www.postgresql.org/mailpref/pgsql-performance> >
[PERFORM] "VACUUM FULL ANALYZE" vs. Autovacuum Contention
Hello, (Apologies if this is an obvious question. I have gone through the archives without seeing something that directly ties to this.) We are running Postgresql on a 64b RHEL5.2 64b server. "Uname -a": --Linux xxx 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:15 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux We have autovacuum enabled with the following settings: autovacuum_naptime = 30s autovacuum_vacuum_threshold = 200 autovacuum_vacuum_scale_factor = 0.5 autovacuum_vacuum_cost_delay = 10 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. 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., -2011-05-07 03:51:04.959 EDT--[unknown]-[unknown] [3348]LOG: connection received: host=##.##.##.## port=60470 -2011-05-07 03:51:04.959 EDT-##.##.##.##-- [3348]LOG: connection authorized: user= database= -2011-05-07 03:51:04.961 EDT-##.##.##.##-- [3348]LOG: statement: VACUUM FULL ANALYZE; -... -2011-05-07 03:51:10.733 EDT--- [19879]ERROR: canceling autovacuum task -2011-05-07 03:51:10.733 EDT--- [19879]CONTEXT: automatic vacuum of table ".xxx." -... -2011-05-07 03:52:48.918 EDT-##.##.##.##-- [3348]LOG: duration: 103957.270 ms -2011-05-07 03:52:48.920 EDT-##.##.##.##-- [3348]LOG: disconnection: session time: 0:01:43.961 user= database= host=##.##.##.## port=60470 We would like to eliminate this error. A bigger problem is that sometimes it seems like autovacuum wins out over "vacuum full analyze". This tends to result in a hung job on our client, with other ensuing complications. * Our basic question is what method we might be able to use to prevent either of these jobs from canceling. What we would like is, instead of autovacuum canceling, it rather always defers to "vacuum full analyze" job, waiting for it to complete. 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). Does that sound right? (If, what might be a good value to set?) Or perhaps there is a more foolproof way of doing this that does not rely upon guesswork? Any suggestions at all would be most welcome! Daniel C.
