Re: Default setting for autovacuum_freeze_max_age

On 10/21/2016 10:29 AM, Robert Haas wrote:
> 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.

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.


-- 
--
Josh Berkus
Red Hat OSAS
(any opinions are my own)