Обсуждение: tuning auto vacuum for highly active tables
Hi All,
We have a postgres database in which couple of tables get bloated due to heavy inserts and deletes. Auto vacuum is running. My question is how can I make auto vacuum more aggressive? I am thinking of enabling autovacuum_vacuum_cost_delay and autovacuum_vacuum_cost_limit parameters. Can anyone suggest how to calculate the appropriate values for these parameters and if there are any side effects of enabling these parameters. Any help will be highly appreciated.
Thanks
Paramjeet Kaur
On Tue, Mar 23, 2010 at 2:54 PM, Bhella Paramjeet-PFCW67 <PBhella@motorola.com> wrote: > Hi All, > > > > We have a postgres database in which couple of tables get bloated due to > heavy inserts and deletes. Auto vacuum is running. My question is how can I > make auto vacuum more aggressive? I am thinking of enabling > autovacuum_vacuum_cost_delay and autovacuum_vacuum_cost_limit parameters. > Can anyone suggest how to calculate the appropriate values for these > parameters and if there are any side effects of enabling these parameters. > Any help will be highly appreciated. OK, autovacuum runs x number of threads, and these threads can have their IO impact limited by cost delay and cost limit. Your first choice is based a lot on your db needs. If you have a lot of large tables that all need to be vacuumed a lot, then you might want to first increase the number of threads before making any of them more aggressive. Then you might want to make the vacuums more aggressive by lower cost_delay down from 20 to 10 or 5 or so milliseconds. On our servers we run 6 threads with a cost_delay of 3 or 4 milliseconds, and autovacuum keeps up without getting in the way. We have a decent DAS array, so we can handle a lot of vacuum threads running at once before they become an issue. The smaller your disk set, the less you can throw vacuum at it and not expect it to mess up the rest of the app. It's all a trade off, but if you don't have more than a disk or two to throw at your db don't expect vacuum to keep up with really heavy activity without impacting your system's performance.
we ran into the same problem, had big table, played with vacuum cost and delay, but can't shrink too much because of heavy insert and delete. we ended up with using slony for upgrade, also have data copy from fresh because of inital replication to shrink our large table, with minimum controlled downtime. Bhella Paramjeet-PFCW67 wrote: > > Hi All, > > > > We have a postgres database in which couple of tables get bloated due > to heavy inserts and deletes. Auto vacuum is running. My question is > how can I make auto vacuum more aggressive? I am thinking of enabling > autovacuum_vacuum_cost_delay and autovacuum_vacuum_cost_limit > parameters. Can anyone suggest how to calculate the appropriate values > for these parameters and if there are any side effects of enabling > these parameters. Any help will be highly appreciated. > > > > Thanks > > Paramjeet Kaur >
we ran into the same problem, had big table, played with vacuum cost and delay, but can't shrink too much because of heavy insert and delete. we ended up with using slony for upgrade, also have data copy from fresh because of inital replication to shrink our large table, with minimum controlled downtime. Bhella Paramjeet-PFCW67 wrote: > > Hi All, > > > > We have a postgres database in which couple of tables get bloated due > to heavy inserts and deletes. Auto vacuum is running. My question is > how can I make auto vacuum more aggressive? I am thinking of enabling > autovacuum_vacuum_cost_delay and autovacuum_vacuum_cost_limit > parameters. Can anyone suggest how to calculate the appropriate values > for these parameters and if there are any side effects of enabling > these parameters. Any help will be highly appreciated. > > > > Thanks > > Paramjeet Kaur >
Hi Scott, Thanks for replying. Can you explain what you mean by increase the number of threads or how I can increase the number of threads? I just have2 tables that are very active. I am using postgres version 8.2.7 and 3510 storagetek array with 10 disks in raid 1+0. Thanks Paramjeet Kaur -----Original Message----- From: Scott Marlowe [mailto:scott.marlowe@gmail.com] Sent: Tuesday, March 23, 2010 2:42 PM To: Bhella Paramjeet-PFCW67 Cc: pgsql-admin@postgresql.org; pgsql-performance@postgresql.org Subject: Re: [ADMIN] tuning auto vacuum for highly active tables On Tue, Mar 23, 2010 at 2:54 PM, Bhella Paramjeet-PFCW67 <PBhella@motorola.com> wrote: > Hi All, > > > > We have a postgres database in which couple of tables get bloated due to > heavy inserts and deletes. Auto vacuum is running. My question is how can I > make auto vacuum more aggressive? I am thinking of enabling > autovacuum_vacuum_cost_delay and autovacuum_vacuum_cost_limit parameters. > Can anyone suggest how to calculate the appropriate values for these > parameters and if there are any side effects of enabling these parameters. > Any help will be highly appreciated. OK, autovacuum runs x number of threads, and these threads can have their IO impact limited by cost delay and cost limit. Your first choice is based a lot on your db needs. If you have a lot of large tables that all need to be vacuumed a lot, then you might want to first increase the number of threads before making any of them more aggressive. Then you might want to make the vacuums more aggressive by lower cost_delay down from 20 to 10 or 5 or so milliseconds. On our servers we run 6 threads with a cost_delay of 3 or 4 milliseconds, and autovacuum keeps up without getting in the way. We have a decent DAS array, so we can handle a lot of vacuum threads running at once before they become an issue. The smaller your disk set, the less you can throw vacuum at it and not expect it to mess up the rest of the app. It's all a trade off, but if you don't have more than a disk or two to throw at your db don't expect vacuum to keep up with really heavy activity without impacting your system's performance.
On Tue, Mar 23, 2010 at 5:28 PM, Bhella Paramjeet-PFCW67 <PBhella@motorola.com> wrote: > Hi Scott, > > Thanks for replying. > Can you explain what you mean by increase the number of threads or how I can increase the number of threads? I just have2 tables that are very active. I am using postgres version 8.2.7 and 3510 storagetek array with 10 disks in raid 1+0. Sure, if you psql into your db and do: show autovac and hit tab a couple times you'll see a list of all these configuration options. The one we're looking for is autovacuum_max_workers. Setting this to something higher will allow that many threads to run at once. While 6 or 8 threads at 5 or 10 milliseconds delay is ok on a bigger RAID array, it'll kill the perf of a machine with a pair of disks in a RAID-1. As you drop the cost_delay, you can no longer run as many threads without starving your machine of IO. It's a good idea to keep track of how many vacuum threads you're usually running and how long they run for (pg_stat_activity can shed some light there). What you're trying to do is get enough threads running so any large tables that take a long time (half hour or more maybe) to vacuum don't get in the way of all the other tables getting vacuumed too. If you've got 2 really big tables and the rest aren't so big, then three threads is likely plenty. If you've got 40 really big tables that take a long time to get vacuumed, then you might need more than just 3 threads. Use iostat -x 10 /dev/sdx to monitor the db arrays to see how much IO you're utilizing with x autovac threads running, then increase it and keep an eye on it, all while running under a fairly steady production load. If going from 3 to 4 threads makes the average utilization go up by 5% then you have an idea how much each thread is costing you. Changing cost_delay OR cost_limit will directly affect how much IO is getting thrown to autovacuum. Lower values of cost_delay and higher values of cost_limit will cost you more in terms of autovacuum daemon using up IO. You really don't want it using up too much of your IO. I shoot for something in the 10% range max, maybe a bit more. Then you want to keep an eye on table bloat to see if vacuum is keeping up. If it's falling behind vacuum verbose as superuser will give you an idea. > > Thanks > Paramjeet Kaur > > -----Original Message----- > From: Scott Marlowe [mailto:scott.marlowe@gmail.com] > Sent: Tuesday, March 23, 2010 2:42 PM > To: Bhella Paramjeet-PFCW67 > Cc: pgsql-admin@postgresql.org; pgsql-performance@postgresql.org > Subject: Re: [ADMIN] tuning auto vacuum for highly active tables > > On Tue, Mar 23, 2010 at 2:54 PM, Bhella Paramjeet-PFCW67 > <PBhella@motorola.com> wrote: >> Hi All, >> >> >> >> We have a postgres database in which couple of tables get bloated due to >> heavy inserts and deletes. Auto vacuum is running. My question is how can I >> make auto vacuum more aggressive? I am thinking of enabling >> autovacuum_vacuum_cost_delay and autovacuum_vacuum_cost_limit parameters. >> Can anyone suggest how to calculate the appropriate values for these >> parameters and if there are any side effects of enabling these parameters. >> Any help will be highly appreciated. > > OK, autovacuum runs x number of threads, and these threads can have > their IO impact limited by cost delay and cost limit. > > Your first choice is based a lot on your db needs. If you have a lot > of large tables that all need to be vacuumed a lot, then you might > want to first increase the number of threads before making any of them > more aggressive. Then you might want to make the vacuums more > aggressive by lower cost_delay down from 20 to 10 or 5 or so > milliseconds. > > On our servers we run 6 threads with a cost_delay of 3 or 4 > milliseconds, and autovacuum keeps up without getting in the way. We > have a decent DAS array, so we can handle a lot of vacuum threads > running at once before they become an issue. > > The smaller your disk set, the less you can throw vacuum at it and not > expect it to mess up the rest of the app. It's all a trade off, but > if you don't have more than a disk or two to throw at your db don't > expect vacuum to keep up with really heavy activity without impacting > your system's performance. > -- When fascism comes to America, it will be intolerance sold as diversity.
Scott Marlowe escribió: > On Tue, Mar 23, 2010 at 5:28 PM, Bhella Paramjeet-PFCW67 > <PBhella@motorola.com> wrote: > > Hi Scott, > > > > Thanks for replying. > > Can you explain what you mean by increase the number of threads or how I can increase the number of threads? I just have2 tables that are very active. I am using postgres version 8.2.7 and 3510 storagetek array with 10 disks in raid 1+0. > > Sure, if you psql into your db and do: > > show autovac > > and hit tab a couple times you'll see a list of all these > configuration options. The one we're looking for is > autovacuum_max_workers. Setting this to something higher will allow > that many threads to run at once. While 6 or 8 threads at 5 or 10 > milliseconds delay is ok on a bigger RAID array, it'll kill the perf > of a machine with a pair of disks in a RAID-1. As you drop the > cost_delay, you can no longer run as many threads without starving > your machine of IO. It's a good idea to keep track of how many vacuum > threads you're usually running and how long they run for > (pg_stat_activity can shed some light there). Hmm, keep in mind that having more workers means that each one of them increments its cost_delay so that the total is roughly what you configured. Also, keep in mind that max_workers is a new setting in 8.3. Since the OP is running 8.2, he can only get one "worker". Presumable he needs to disable autovac for those two very active tables and setup a cron job to process them in their own schedule. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.
Alvaro Herrera escribió: > Also, keep in mind that max_workers is a new setting in 8.3. Since the > OP is running 8.2, he can only get one "worker". Presumable he needs to > disable autovac for those two very active tables and setup a cron job to > process them in their own schedule. Err, sorry, "she", not "he". -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.