| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
| Cc: | Scott Carey <scott(at)richrelevance(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Kenneth Cox <kenstir(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Advice configuring ServeRAID 8k for performance |
| Date: | 2010-08-16 20:02:27 |
| Message-ID: | 20100816200227.GA3911@anarazel.de |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-performance |
On Mon, Aug 16, 2010 at 01:46:21PM -0400, Greg Smith wrote:
> Scott Carey wrote:
> >This is because an fsync on ext3 flushes _all dirty pages in the file system_ to disk, not just those for the file being fsync'd.
> >One partition for WAL, one for data. If using ext3 this is
> >essentially a performance requirement no matter how your array is
> >set up underneath.
>
> Unless you want the opposite of course. Some systems split out the
> WAL onto a second disk, only to discover checkpoint I/O spikes
> become a problem all of the sudden after that. The fsync calls for
> the WAL writes keep the write cache for the data writes from ever
> getting too big. This slows things down on average, but makes the
> worst case less stressful. Free lunches are so hard to find
> nowadays...
Or use -o sync. Or configure a ridiciuosly low dirty_memory amount
(which has a problem on large systems because 1% can still be too
much. Argh.)...
Andres
| From | Date | Subject | |
|---|---|---|---|
| Next Message | Greg Smith | 2010-08-16 20:13:22 | Re: Advice configuring ServeRAID 8k for performance |
| Previous Message | Greg Smith | 2010-08-16 17:46:21 | Re: Advice configuring ServeRAID 8k for performance |