On Fri, Oct 21, 2016 at 1:17 PM, Josh Berkus <josh@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.
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."
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
