On Thu, Oct 27, 2016 at 6:55 AM, Josh Berkus <j...@agliodbs.com> wrote: > On 10/21/2016 10:29 AM, Robert Haas wrote: >> On Fri, Oct 21, 2016 at 1:17 PM, Josh Berkus <j...@agliodbs.com> wrote: >>> Particularly, with 9.6's freeze map, point (2) is even stronger reason >>> to *lower* autovacuum_max_freeze_age. Since there's little duplicate >>> work in a freeze scan, a lot of users will find that frequent freezing >>> benefits them a lot ... >> >> That's a very good point, although I hope that vacuum is mostly being >> triggered by vacuum_freeze_table_age rather than >> autovacuum_freeze_max_age. > > Well, depends on the nature of writes to the table. For insert-mostly > tables, vacuum_freeze_table_age is pretty much never triggered. Isn't > there a patch for that somewhere? > >> >> On Bruce's original question, there is an answer written into our >> documentation: "Vacuum also allows removal of old files from the >> pg_clog subdirectory, which is why the default is a relatively low 200 >> million transactions." > > Point.
It also affects pg_commit_ts size (if enabled), and it uses 40x more space per xid than pg_clog if I've read the code right. I have wondered before if we should document that.  https://www.postgresql.org/message-id/CAEepm=3pm05_t__3psxbacdlm7wwmyrbr_3myfcke2trkxk...@mail.gmail.com -- Thomas Munro http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers