Re: Visibility map and freezing

Jeff Davis wrote:
> On Fri, 2009-01-09 at 13:49 +0200, Heikki Linnakangas wrote:
> If the distinction you're making is that autovacuum_freeze_max_age
> affects the launching of a vacuum rather than the behavior of a vacuum,
> maybe we could incorporate the word "launch" like:
>
> autovacuum_launch_freeze_threshold

Hmm, I think I'd like it in the form autovacuum_freeze_launch_threshold
more.

>> I'm now leaning towards:
>>
>> autovacuum_freeze_max_age
>> vacuum_freeze_table_age
>> vacuum_freeze_min_age
>>
>> where autovacuum_freeze_max_age and vacuum_freeze_min_age are unchanged,
>> and vacuum_freeze_table_age is the new setting that controls when VACUUM
>> or autovacuum should perform a full scan of the table to advance
>> relfrozenxid.
>
> I'm still bothered by the fact that "max" and "min" really mean the same
> thing here.

Yeah. Those are existing names, though, and I don't recall any
complaints from users.

> I don't think we can perfectly capture the meaning of these GUCs in the
> name. I think our goal should be to avoid confusion between them.

Agreed.

Well, for better or worse here's a patch leaving the existing setting
names alone, and the new GUC is called "vacuum_freeze_table_age". I'm
not opposed to changing the names of the existing GUCs. If we do change
them, the columns in pg_autovacuum need to be changed too.

There's documentation changes included to descríbe the new GUC, and the
new behavior of VACUUM with visibility map in general. Is it readable,
and is it enough?

Alvaro, are you getting rid of pg_autovacuum in favor of the reloptions
for 8.4? This patch adds a new column to pg_autovacuum, reflecting the
new vacuum_freeze_table_age GUC just like freeze_min_age column reflects
vacuum_freeze_min_age. If I commit this tomorrow, will I cause you a lot
of trouble with the reloptions patch?

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com