Re: [ovirt-devel] [ovirt-users] [Feture discussion] Full vacuum tool

On 7 December 2016 at 21:44, Roy Golan <rgolan(a)redhat.com&gt; wrote: > > > On 7 December 2016 at 21:00, Michal Skrivanek <mskrivan(a)redhat.com&gt; > wrote: > >> >> >> On 07 Dec 2016, at 11:28, Yaniv Kaul <ykaul(a)redhat.com&gt; wrote: >> >> >> >> On Wed, Dec 7, 2016 at 10:57 AM, Roy Golan <rgolan(a)redhat.com&gt; wrote: >> >>> Hi all, >>> >>> This is a discussion on the RFE[1] to provide a tool to perform full >>> vacuum on our DBs. >>> >>> First if you are not familiar with vacuum please read this [2] >>> >>> # Backgroud >>> ovirt 'engine' DB have several busy table with 2 differnt usage patten. >>> One is audit_log and the others are the 'v*_statistics' tables and the >>> difference between them is mostly inserts vs mostly hot updates. >>> Tables with tons of updates creates garbage or 'dead' records that >>> should be removed, and for this postgres have the aforementioned autovacuum >>> cleaner. It will make the db reuse its already allocated space to perform >>> future updates/inserts and so on. >>> Autovacuum is essential for a db to function optimally and tweaking it >>> is out of the scope of the feature. >>> >>> Full vacuum is designed to reclaim the disk space and reset the table >>> statistics. It is a heavy maintenance task, it takes an exclusive lock on >>> the table and may take seconds to minutes. In some situations it is >>> effectively a downtime due to the long table lock and should not be running >>> when the engine is running. >>> >> >> So, effectively this should be interesting mostly/only for the audit >> log. All other busy table are mostly in-place updates >> > > Given that autovacuum is performing well the yes but if it starts to fall > behind this may help a bit. > audit_log is insert mostly and also delete, we remove a day, each day. > >> >> >>> # Critiria >>> Provide a way to reclaim disk space claimed by the garbage created over >>> time by the engine db and dwh. >>> >>> # Usage >>> Either use it as part of the upgrade procedure (after all dbscipts >>> execution) >>> >> >> That does sound as a good start not requiring much user involvement >> >> or just provide the tool and admin will run in on demand >>> - engine db credentials read from /etc/ovirt-engine/engine.conf.d/ >>> - invocation: >>> ``` >>> tool: [dbname(default engine)] [table: (default all)] >>> ``` >>> - if we invoke it on upgrade than an installation plugin should be >>> added to invoke with default, no interaction >>> >> >> +1 >> >> - since VACUUM ANALYZE is consider a recommended maintenance task we can >>> to it by default and ask the user for FULL. >>> >> >> When would you run it? ANALYZE nightly? >> >> No I'd still avoid doing this repeatedly, autovaccum should handle that > as well, but this would cover situations where it isn't functioning > optimally. > > I think its worth adding a report of the db status and the rate of the > autovacuum (a slight midifed version of the query mskrivanek ran on one of > the production systems [3]) that will go to the logcollector. Perhaps the > output of the ANALYZE will help as well. > > [3] https://gist.github.com/rgolangh/049cff30b89c5b29284ceee80a3 > 5dbb4#file-table_status_by_dead_rows-sql > Very interesting collection of pg scrips to measure bloat and vacuum - needs access to postgres objects though - https://github.com/pgexperts/pgx_scripts - https://github.com/pgexperts/pgx_scripts/blob/master/bloat/ table_bloat_check.sql - https://github.com/pgexperts/pgx_scripts/blob/master/ vacuum/last_autovacuum.sql > > >>> >> Will the user know to answer intelligently if vacuum is needed or not? >> Except for 'yes, you need it', we cannot even provide a time estimate (I >> assume a disk space estimate is available!) >> >> perhaps we can estimate the bloat, there should be a github script to > calculate that [4] not sure how good it is. > >> I would suggest to run ANALYZE for sure and provide an option at the end >> of installation, to run the required command line - so make it as >> accessible as possible, but not part of the flow. >> >> >> If there are no significant gains why bother any other time but on >> upgrade when it can be run unconditionally? >> >> >> I'm wondering if the community can run ANALYZE on their database, and we >> can estimate how many are in dire need for full vacuum already. >> Y. >> >> I'll send a different mail for that. > > >> >> - remote db is supported as well, doesn't have to be local >>> >> >> Well, not sure if we need to bother. It was introduced for large >> deployments where the host can't fit both engine and db load. Do we still >> have this issue? I wouldn't say so for 4.1. It may be very niche case >> >> Running full vacuum is anyway a psql command, so there is no hidden cost > here (to the development side I mean) > > >> Thanks, >> michal >> >> >>> # Questions >>> - Will remote dwh have the credentials under >>> /etc/ovirt-engine/engine.conf.d? >>> - Should AAA schema be taken into account as well? >>> >>> Please review, thanks >>> Roy >>> >>> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1388430 >>> [2] https://www.postgresql.org/docs/9.2/static/runtime-config-au >>> tovacuum.html >>> [3] https://www.postgresql.org/docs/devel/static/sql-vacuum.html >>> >>> _______________________________________________ >>> Users mailing list >>> Users(a)ovirt.org >>> http://lists.ovirt.org/mailman/listinfo/users >>> >>> >> _______________________________________________ >> Users mailing list >> Users(a)ovirt.org >> http://lists.ovirt.org/mailman/listinfo/users >> >> > _______________________________________________ Devel mailing list Devel(a)ovirt.org http://lists.ovirt.org/mailman/listinfo/devel