Re: [HACKERS] O_DIRECT for WAL writes - Mailing list pgsql-patches

From Bruce Momjian
Subject Re: [HACKERS] O_DIRECT for WAL writes
Date
Msg-id 200508112036.j7BKaAX09363@candle.pha.pa.us
Whole thread Raw
In response to Re: [HACKERS] O_DIRECT for WAL writes  (Mark Wong <markw@osdl.org>)
List pgsql-patches
Mark Wong wrote:
> Ok, I finally got a couple of tests done against CVS from Aug 3, 2005.
> I'm not sure if I'm showing anything insightful though.  I've learned
> that fdatasync and O_DSYNC are simply fsync and O_SYNC respectively on
> Linux, which you guys may have already known.  There appears to be a

That is not what we thought for Linux, but many other OS's behave that
way.

> fair performance decrease in using open_sync.  Just to double check, am
> I correct in understanding only open_sync uses O_DIRECT?

Right.

> fdatasync
> http://www.testing.osdl.org/projects/dbt2dev/results/dev4-015/38/
> 5462 notpm
>
> open_sync
> http://www.testing.osdl.org/projects/dbt2dev/results/dev4-015/40/
> 4860 notpm

Right now open_sync is our last choice, which seems to still be valid
for Linux, at least.

--
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  pgman@candle.pha.pa.us               |  (610) 359-1001
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