| From: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
|---|---|
| To: | Marti Raudsepp <marti(at)juffo(dot)org> |
| Cc: | Thomas Pöhler <tp(at)turtle-entertainment(dot)de>, pgsql-performance(at)postgresql(dot)org, Felix Feinhals <ff(at)turtle-entertainment(dot)de>, Verteiler_A-Team <a-team(at)turtle-entertainment(dot)de>, Björn Metzdorf <bm(at)turtle-entertainment(dot)de> |
| Subject: | Re: high user cpu, massive SELECTs, no io waiting problem |
| Date: | 2011-02-16 15:43:06 |
| Message-ID: | AANLkTikb3XJih-O+fJtOsWWAtkq8FG9iCCR8N-_uMXyp@mail.gmail.com |
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| Lists: | pgsql-performance |
On Wed, Feb 16, 2011 at 6:44 AM, Marti Raudsepp <marti(at)juffo(dot)org> wrote:
> On Tue, Feb 15, 2011 at 20:01, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
>> run htop and look for red. if youi've got lots of red bar on each CPU
>> but no io wait then it's waiting for memory access.
>
> I don't think this is true. AFAICT the red bar refers to "system
> time", time that's spent in the kernel -- either in syscalls or kernel
> background threads.
My point being that if you've got a lot of RED it'll be the OS waiting
for memory access. Trust me, when we start to hit our memory
bandwidth (in the 70 to 80 GB/s range) we start to get more and more
red and more and more kernel wait time.
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