| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Curt Sampson <cjs(at)cynic(dot)net> |
| Cc: | "J(dot) R(dot) Nield" <jrnield(at)usol(dot)com>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Michael Loftis <mloftis(at)wgops(dot)com>, mlw <markw(at)mohawksoft(dot)com>, PostgreSQL Hacker <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Index Scans become Seq Scans after VACUUM ANALYSE |
| Date: | 2002-06-23 15:19:15 |
| Message-ID: | 8461.1024845555@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Curt Sampson <cjs(at)cynic(dot)net> writes:
> This should also allow us to disable completely the ping-pong writes
> if we have a disk subsystem that we trust.
If we have a disk subsystem we trust, we just disable fsync on the
WAL and the performance issue largely goes away.
I concur with Bruce: the reason we keep page images in WAL is to
minimize the number of places we have to fsync, and thus the amount of
head movement required for a commit. Putting the page images elsewhere
cannot be a win AFAICS.
> Well, whether or not there's a cheap way depends on whether you consider
> fsync to be cheap. :-)
It's never cheap :-(
regards, tom lane
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