From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Sean Chittenden <sean(at)chittenden(dot)org> |
Cc: | "Jim C(dot) Nasby" <jim(at)nasby(dot)net>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: O_DIRECT in freebsd |
Date: | 2003-06-23 03:26:36 |
Message-ID: | 200306230326.h5N3QaH19248@candle.pha.pa.us |
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Lists: | pgsql-hackers |
Sean Chittenden wrote:
> Nor could it ever be a win unless the cache was populated via
> O_DIRECT, actually. Big PG cache == 2 extra copies of data, once in
> the kernel and once in PG. Doing caching at the kernel level, however
> means only one copy of data (for the most part). Only problem with
> this being that it's not always that easy or an option to reconfig a
> kernel to have a bigger FS cache. That said, tripple copying a chunk
> of mem is generally faster than even a single disk read. If
> PostgreSQL ever wanted to have a platform agnostic way of doing
> efficient caching, it'd likely have to be in the userland and would
> require the use of O_DIRECT.
Actually, I think of O_DIRECT as platform-dependent.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
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