Hi, On Thu, Mar 28, 2019 at 12:36:24PM +1300, David Rowley wrote: > On Thu, 28 Mar 2019 at 11:01, Alvaro Herrera <alvhe...@2ndquadrant.com> wrote: > > I wonder if Mandrill's problem is related to Mailchimp raising the > > freeze_max_age to a point where autovac did not have enough time to > > react with an emergency vacuum. If you keep raising that value because > > the vacuums cause problems for you (they block DDL), there's something > > wrong. > > I have seen some very high autovacuum_freeze_max_age settings > recently. It would be interesting to know what they had theirs set to. > I see they mentioned "Search and Url tables". I can imagine "search" > never needs any UPDATEs, so quite possibly those were append-only, in > which case the anti-wraparound vacuum would have had quite a lot of > work on its hands since possibly every page needed frozen. A table > receiving regular auto-vacuums from dead tuples would likely get some > pages frozen during those.
By the way, the Routine Vacuuming chapter of the documentation says: "The sole disadvantage of increasing autovacuum_freeze_max_age (and vacuum_freeze_table_age along with it) is that the pg_xact and pg_commit_ts subdirectories of the database cluster will take more space [...] If [pg_xact and pg_commit_ts taking 0.5 and 20 GB, respectively] is trivial compared to your total database size, setting autovacuum_freeze_max_age to its maximum allowed value is recommended." Maybe this should be qualified with "unless you have trouble with your autovacuum keeping up" or so; or generally reworded? Michael
