| From: | Mark Kirkwood <mark(dot)kirkwood(at)catalyst(dot)net(dot)nz> |
|---|---|
| To: | Josh Berkus <josh(at)agliodbs(dot)com> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: High CPU usage / load average after upgrading to Ubuntu 12.04 |
| Date: | 2013-02-19 23:37:38 |
| Message-ID: | 51240CC2.8060609@catalyst.net.nz |
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| Thread: | |
| Lists: | pgsql-performance |
On 20/02/13 12:24, Josh Berkus wrote:
>
> NM, I tested lowering dirty_background_ratio, and it didn't help,
> because checkpoints are kicking in before pdflush ever gets there.
>
> So the issue seems to be that if you have this combination of factors:
>
> 1. large RAM
> 2. many/fast CPUs
> 3. a database which fits in RAM but is larger than the RAID controller's
> WB cache
> 4. pg_xlog on the same volume as pgdata
>
> ... then you'll see checkpoint "stalls" and spread checkpoint will
> actually make them worse by making the stalls longer.
>
> Moving pg_xlog to a separate partition makes this better. Making
> bgwriter more aggressive helps a bit more on top of that.
>
We have pg_xlog on a pair of PCIe SSD. Also we running the deadline io
scheduler.
Regards
Mark
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