Re: [HACKERS] high shared buffer and swap

On Tue, May 5, 2009 at 11:15 AM, PFC <lists@peufeu.com> wrote:
>
>> An octocore server with 32GB of ram, running postgresql 8.3.6
>> Running only postgresql, slony-I and pgbouncer.
>>
>> Just for testing purpose, i tried a setting with 26GB of shared_buffer.
>>
>> I quickly noticed that the performances wasn't very good and the
>> server started to swap slowly but surely.
>>  (but still up to 2000query/second as reported by pgfouine)
>>
>> It used all the 2GB of swap.
>> I removed the server from production, added 10GB of swap and left it
>> for the weekend with only slony and postgresql up to keep it in sync
>> with the master database.
>>
>> This morning i found that the whole 12GB of swap were used :
>
> Hm, do you really need swap with 32Gb of RAM ?
> One could argue "yes but swap is useful to avoid out of memory
> errors".
> But if a loaded server starts to swap a lot, it is as good as dead
> anyway...

Not really, but we have it.
I tried with swappinness set to 0 and ... it swaps !

I'm back to 4GB of shared_buffer :)
I'll try various setting, maybe 16GB, etc ...
But my goal was to avoid OS filesystem cache and usage of
shared_buffer instead : FAIL.

--
F4FQM
Kerunix Flan
Laurent Laborde