Re: High load,

On Thu, Jan 27, 2011 at 10:54 AM, Stephen Frost <sfrost@snowman.net> wrote:
> * Michael Kohl (michael.kohl@tupalo.com) wrote:
>> HDD: 2x 120 GB OCZ Vertex 2 SSD; RAID 1
>
> I'm amazed no one else has mentioned this yet, but you should look into
> splitting your data and your WALs.  Obviously, having another set of
> SSDs to put your WALs on would be ideal.

Actually spinning media would be a better choice.  A pair of fast
15krpm drives in a mirror will almost always outrun an SSD for
sequential write speed.  Even meh-grade 7200RPM SATA drives will win.

> You should probably also be looking into adjustments to the background
> writer.  It sounds like you're getting hit by large checkpoint i/o
> (if you turn on logging of that, as someone else suggested, you'll be
> able to corrollate the times), which can be helped by increasing the
> amount of writing done between checkpoints, so that the checkpoints
> aren't as big and painful.  That can be done by making the background
> writer more aggressive.

This++.  Increasing checkpoint segments can make a huge difference.
We run 64 segments in production and it's a world of difference from
the stock setting.