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Re: concurrent IO in postgres?

From: Przemek Wozniak <wozniak(at)lanl(dot)gov>
To: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: concurrent IO in postgres?
Date: 2010-12-23 19:46:57
Message-ID: 1293133617.3685.97.camel@procyon.lanl.gov (view raw or flat)
Thread:
Lists: pgsql-performance
On Thu, 2010-12-23 at 11:24 -0700, Scott Marlowe wrote:
> On Thu, Dec 23, 2010 at 10:37 AM, Przemek Wozniak <wozniak(at)lanl(dot)gov> wrote:
> > When testing the IO performance of ioSAN storage device from FusionIO
> > (650GB MLC version) one of the things I tried is a set of IO intensive
> > operations in Postgres: bulk data loads, updates, and queries calling
> > for random IO. So far I cannot make Postgres take advantage of this
> 
> So, were you running a lot of these at once?  Or just single threaded?

> I get very good io concurrency with lots of parallel postgresql
> connections on a 34 disk SAS setup with a battery backed controller.

In one test I was running between 1 and 32 clients simultaneously
writing lots of data using copy binary. The problem is that with a large
RAM buffer it all goes there, and then the background writer, a single
postgres process, will issue write requests one at a time I suspect.
So the actual IO is effectively serialized by the backend.



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