Re: Occasional giant spikes in CPU load

On 4/7/10 2:59 PM, Tom Lane wrote:
> Craig James<craig_james(at)emolecules(dot)com> writes:
>> Most of the time Postgres runs nicely, but two or three times a day we get a huge spike in the CPU load that lasts just a short time -- it jumps to 10-20 CPU loads. Today it hit 100 CPU loads. Sometimes days go by with no spike events. During these spikes, the system is completely unresponsive (you can't even login via ssh).
>> I managed to capture one such event using top(1) with the "batch" option as a background process. See output below - it shows 19 active postgress processes, but I think it missed the bulk of the spike.
>
>> Any ideas where I can look to find what's triggering this?
>
>> Postgres 8.3.0
> ^^^^^
>
> If it's really 8.3.0, try updating to 8.3.something-recent. We've fixed
> a whole lot of bugs since then.

Good advice, I've been meaning to do this, maybe this will be a kick in the pants to motivate me.

> I have a suspicion that this might be an sinval overrun scenario, in
> which case you'd need to update to 8.4 to get a real fix. But updating
> in the 8.3 branch would be cheap and easy.
>
> If it is sinval overrun, it would presumably be triggered by a whole lot
> of catalog changes being made at approximately the same time. Can you
> correlate the spikes with anything like that?

Not that I know of. Just regular web traffic. On the backup server these events happen occasionally even when there is little or no web traffic, and nobody logged in doing maintenance.

>
> regards, tom lane
>