Josh Berkus wrote: > On 04/15/2014 02:25 PM, Josh Berkus wrote: > > Hackers, > > > > We need documentation on how users should intelligently set the > > multixact freeze settings. I'm happy to write the actual text, but I > > definitely don't have any idea how to set these myself. Under what > > circumstances should they be different from freeze_max_age? How?
Measure consumption rate of multixacts, compare to consumption rate of xids, and set the freeze ages so that they are reached more-or-less at the same time, so that freezing for any of them would also freeze the other one. You need to set both table_freeze_ages to values that would be reached later than both min_freeze_ages would be reached, if you get what I mean. The idea is that full scan of a table would fix both things at once, saving a followup full scan shortly after the first one. You can see the current multixact value in pg_controldata output. Keep timestamped values of that somewhere (a table?) so that you can measure consumption rate. I don't think we provide SQL-level access to those values. > Also: how do I check the multixact age of a table? There doesn't seem > to be any data for this ... pg_class.relminmxid is the oldest multixact value that might be present in a table. -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers