Re: Occasional giant spikes in CPU load - Mailing list pgsql-performance

From David Rees
Subject Re: Occasional giant spikes in CPU load
Date
Msg-id z2v72dbd3151004071652oce71dc69n6dea759617e4be@mail.gmail.com
Whole thread Raw
In response to Re: Occasional giant spikes in CPU load  (Craig James <craig_james@emolecules.com>)
List pgsql-performance
On Wed, Apr 7, 2010 at 3:57 PM, Craig James <craig_james@emolecules.com> wrote:
> On 4/7/10 3:36 PM, Joshua D. Drake wrote:
>> My guess is that it is not CPU, it is IO and your CPU usage is all WAIT
>> on IO.
>>
>> To have your CPUs so flooded that they are the cause of an inability to
>> log in is pretty suspect.
>
> I thought so too, except that I can't login during the flood.  If the CPUs
> were all doing iowaits, logging in should be easy.

No - logging in with high iowait is very harder to do than high CPU
time because of latency of disk access.

> Greg's suggestion that shared_buffers and work_mem are too big for an 8 GB
> system fits these symptoms -- if it's having a swap storm, login is
> effectively impossible.

A swap storm effectively puts the machine into very high iowait time.

-Dave

pgsql-performance by date:

Previous
From: Steve Crawford
Date:
Subject: Re: Occasional giant spikes in CPU load
Next
From: Tom Lane
Date:
Subject: Re: Occasional giant spikes in CPU load