Also read about hot updates and the storage parameter named "fill_factor", so, data blocks can be recycled instead of creating new ones if the updated fields don't update also indexes.
Am Mi., 5. Dez. 2018 um 09:39 Uhr schrieb Alexey Bashtanov <bashta...@imap.cc>: > > > > > The table has around 1.5M rows which have been updated/inserted around > > 121M times, the distribution of updates to row in alerts_alert will be > > quite uneven, from 1 insert up to 1 insert and 0.5M updates. > > > > Under high load (200-300 inserts/updates per second) we see occasional > > (~10 per hour) updates taking excessively long times (2-10s). These > > updates are always of the form: > > > > UPDATE "alerts_alert" SET ...bunch of fields... WHERE > > "alerts_alert"."id" = '...sha1 hash...'; > > > > Here's a sample explain: > > > > https://explain.depesz.com/s/Fjq8 > > > > What could be causing this? What could we do to debug? What config > > changes could we make to alleviate this? > > > > Hello Chris, > > One of the reasons could be the row already locked by another backend, > doing the same kind of an update or something different. > Are these updates performed in a longer transactions? > Can they hit the same row from two clients at the same time? > Is there any other write or select-for-update/share load on the table? > > Have you tried periodical logging of the non-granted locks? > Try querying pg_stat_activity and pg_locks (possibly joined and maybe > repeatedly self-joined, google for it) > to get the backends that wait one for another while competing for to > lock the same row or object. > > Best, > Alex > > -- El genio es 1% inspiración y 99% transpiración. Thomas Alva Edison http://pglearn.blogspot.mx/
