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Re: High load,

From: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
To: Stephen Frost <sfrost(at)snowman(dot)net>
Cc: Michael Kohl <michael(dot)kohl(at)tupalo(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: High load,
Date: 2011-01-27 18:13:17
Message-ID: AANLkTikTSkGKNXdqJOP_D78mXSRv-NXMZUnd4Q80qqwv@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Thu, Jan 27, 2011 at 10:54 AM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> * Michael Kohl (michael(dot)kohl(at)tupalo(dot)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.

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