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                      
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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