| From: | Marti Raudsepp <marti(at)juffo(dot)org> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-performance(at)postgresql(dot)org, Greg Smith <greg(at)2ndquadrant(dot)com> |
| Subject: | Re: Defaulting wal_sync_method to fdatasync on Linux for 9.1? |
| Date: | 2010-11-17 00:01:21 |
| Message-ID: | AANLkTim2v2fvzY0h8wwgiULTpPB=-SNVYQKPU0Xf3__G@mail.gmail.com |
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| Lists: | pgsql-performance |
On Wed, Nov 17, 2010 at 01:31, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Well, we're not going to increase the default to gigabytes, but we could
> very probably increase it by a factor of 10 or so without anyone
> squawking. It's been awhile since I heard of anyone trying to run PG in
> 4MB shmmax. How much would a change of that size help?
In my testing, when running a large bulk insert query with fdatasync
on ext4, changing wal_buffers has very little effect:
http://ompldr.org/vNjNiNQ/wal_sync_method1.png
(More details at
http://archives.postgresql.org/pgsql-performance/2010-11/msg00094.php
)
It would take some more testing to say this conclusively, but looking
at the raw data, there only seems to be an effect when moving from 8
to 16MB. Could be different on other file systems though.
Regards,
Marti
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