On 2013-05-24 15:49:31 -0400, Josh Berkus wrote:
> If I understand your solution correctly, though, this doesn't really
> help the pathological case for freezing, which is the time-oriented
> append-only table. For data which isn't being used, allvisible won't be
> set either because it won't have been read, no? Is it still cheaper to
> set allvisible than vacuum freeze even in that case?
all visible is only set in vacuum and it determines which parts of a
table will be scanned in a non full table vacuum. So, since we won't
regularly start vacuum in the insert only case there will still be a
batch of work at once. But nearly all of that work is *already*
performed. We would just what the details of that around for a
bit. *But* since we now would only need to vacuum the non all-visible
part that would get noticeably cheaper as well.
I think for that case we should run vacuum more regularly for insert
only tables since we currently don't do regularly enough which a) increases
the amount of work needed at once and b) prevents index only scans from
working there.
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services