From: | Jignesh Shah <jkshah(at)gmail(dot)com> |
---|---|
To: | Bruce Momjian <bruce(at)momjian(dot)us> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Dimitri Fontaine <dfontaine(at)hi-media(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, postgres performance list <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: PostgreSQL as a local in-memory cache |
Date: | 2010-06-30 00:48:23 |
Message-ID: | AANLkTikj3pglP8uqPdUBHZ3bDQq86aG6MYzDUUyurTez@mail.gmail.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-performance |
On Tue, Jun 29, 2010 at 2:45 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> Tom Lane wrote:
>> Bruce Momjian <bruce(at)momjian(dot)us> writes:
>> >>> I asked on IRC and was told it is true, and looking at the C code it
>> >>> looks true. ?What synchronous_commit = false does is to delay writing
>> >>> the wal buffers to disk and fsyncing them, not just fsync, which is
>> >>> where the commit loss due to db process crash comes from.
>>
>> >> Ah, I see. Thanks.
>>
>> > I am personally surprised it was designed that way; I thought we would
>> > just delay fsync.
>>
>> That would require writing and syncing to be separable actions. If
>> you're using O_SYNC or similar, they aren't.
>
> Ah, very good point. I have added a C comment to clarify why this is
> the current behavior; attached and applied.
>
> --
> Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
> EnterpriseDB http://enterprisedb.com
Though has anybody seen a behaviour where synchronous_commit=off is
slower than synchronous_commit=on ? Again there are two cases here
one with O_* flag and other with f*sync flags. But I had seen that
behavior with PostgreSQL 9.0 beta(2 I think) though havent really
investigated it much yet .. (though now I dont remember which
wal_sync_method flag) . Just curious if anybody has seen that
behavior..
Regards,
Jignesh
From | Date | Subject | |
---|---|---|---|
Next Message | Greg Smith | 2010-06-30 01:23:37 | Re: pgbench results on a new server |
Previous Message | Kevin Grittner | 2010-06-29 21:30:27 | Re: ideal storage configuration |