Bruce Momjian wrote:
>
> Yep, agreed on the random I/O issue. The larger question is if you have
> a huge table, do you care to reclaim 3% of the table size, rather than
> just vacuum it when it gets to 10% dirty? I realize the vacuum is going
> to take a lot of time, but vacuuming to relaim 3% three times seems like
> it is going to be more expensive than just vacuuming the 10% once. And
> vacuuming to reclaim 1% ten times seems even more expensive. The
> partial vacuum idea is starting to look like a loser to me again.
But if the partial vacuum is able to clean the busiest pages and reclaim
useful space, currently-running transactions will be able to use that
space and thus not have to extend the table. Not that extension is a
problem on itself, but it'll keep your working set smaller.
--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support