Re: Restore of pg_dump taking a long time...

Tom Lane wrote:
>
> There's not much you can do to improve the performance of a restore
> already in progress. Next time you might want to think about kicking up
> maintenance_work_mem before you start it; that's about the only thing
> you can really do to speed up index builds.

I have found that increasing maintenance_work_mem can decrease index
build speed on large tables:

maintenance_work_mem 32768 262144 1048576 2097151
---------------------------------------------------------------
index 400M rows (min) 55 61 68 70
index 45M rows (min) 4.03 4.22 4.88 2.55

These timings were done on a machine with 8GB ram and postgresql 8.1.3
(from the RPMs on postgresql.org) Each time is an average of three
runs; before each run, postgres was shut down and the filesystem with
/var/lib/pgsql was remounted to clear the filesystem cache.

I'm assuming that the times are increasing because there is less
memory available for the filesystem cache. Similarly, I assume that
the runs on the smaller table with maintenance_work_mem = 2097151
are faster because everything fits in that space.

-- todd