Re: freezing tuples ( was: Why is vacuum_freeze_min_age 100m? )

Jeff, Tom,

>> Let's say that we had a range like 50-100M, where if it's older than
>> 100M, we freeze it, and if it's older than 50M we freeze it only if it's
>> on a dirty page. We would still have forensic evidence, but we could
>> make a range such that we avoid writing multiple times.
> 
> Yeah, making the limit "slushy" would doubtless save some writes, with
> not a lot of downside.

This would mean two settings: vacuum_freeze_min_age and
vacuum_freeze_dirty_age.  And we'd need to add those to the the
autovacuum settings for each table as well.  While we could just make
one setting 1/2 of the other, that prevents me from saying:

"freeze this table agressively if it's in memory, but wait a long time
to vaccuum if it's on disk"

I can completely imagine a table which has a vacuum_freeze_dirty_age of
10000 and a vacuum_freeze_min_age of 1m.

-- 
Josh Berkus
PostgreSQL Experts Inc.
www.pgexperts.com