Re: checkpoints/bgwriter tuning verification

On Fri, 2009-10-30 at 07:15 -0400, Steve Clark wrote:
> On 10/29/2009 04:42 PM, Scott Marlowe wrote:
> > On Thu, Oct 29, 2009 at 12:46 PM, Vick Khera<vivek(at)khera(dot)org> wrote:
> >> On my primary DB I'm observing random slowness which just doesn't make
> >> sense to me. The I/O system can easily do 40MB/sec writes, but I'm
> >> only seeing a sustained 5MB/sec, even as the application is stalling
> >> waiting on the DB.
> >
> > Just one point on top of everything else you'll hear. 40 MB/sec
> > sequential throughput does not equal 40MB/sec random PLUS checkpoint
> > throughput. Random access is gonna lower that 40MB/sec way down real
> > fast.
> >
> > First step to speed things up is putting pg_xlog on its own disk(s).
> Hi Scott,
>
> How exactly do you do this? By creating a link to the new location or
> is there a config option somewhere that says where the pg_xlog resides?

There is an option to do this during initdb. If you want to do it after
the DB is created, move the contents of pg_xlog/ (when the DB is shut
down) and make a symlink to the new directory.

--
Brad Nicholson 416-673-4106
Database Administrator, Afilias Canada Corp.