Andres Freund <and...@2ndquadrant.com> wrote: > On 2013-01-29 16:09:52 +1100, Josh Berkus wrote: >> >>> I have to admit, I fail to see why this is a good idea. There >>> isn't much of an efficiency bonus in freezing early (due to >>> hint bits) and vacuums over vacuum_freeze_table_age are >>> considerably more expensive as they have to scan the whole heap >>> instead of using the visibilitymap. And if you don't vacuum the >>> whole heap you can't lower relfrozenxid. So changing >>> freeze_min_age doesn't help at all to avoid anti-wraparound >>> vacuums. >>> >>> Am I missing something? >> >> Yep. First, you're confusing vacuum_freeze_table_age and >> vacuum_freeze_min_age. > > Don't think I did. I was talking about vacuum_freeze_table_age > because that influences the amount of full-table scans
Not any more than vacuum_freeze_min_age does. http://www.postgresql.org/docs/9.2/interactive/routine-vacuuming.html#AUTOVACUUM | a whole table sweep is forced if the table hasn't been fully | scanned for vacuum_freeze_table_age minus vacuum_freeze_min_age | transactions. So reducing vacuum_freeze_min_age not only helps minimize the writes that are needed when autovacuum needs to scan the entire heap, but also decreases the frequency of those full-table scans. -Kevin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
