Re: postgresql-8.0.1 performance tuning

Cosimo Streppone wrote:
> Mark Kirkwood ha scritto:
>
>> Cosimo Streppone wrote:
>>
>>> ######### Config ############
>>>
>>>> /etc/sysctl.conf:
>>>> kernel.shmall = 786432000
>>>> kernel.shmmax = 786432000
>>>
>>>
>>> I think you have a problem here.
>>> kernel.shmmax should *not* be set to an amount of RAM, but
>
>
> Sorry, I thought "shmall" but written "shmmax".
> Thanks Mark!
>

Hehe - happens to me all the time!

On the shmall front - altho there is *probably* no real performance
impact setting it to the same as shmmax (i.e. allowing 4096 allocations
of size shmmax!), it is overkill. In addition it does allow for a DOS by
a program that allocates thousands of segments (or somehow starts
thousands of Pg servers on different ports...)!

For a dedicated Pg server I would size shmall using a calculation along
the lines of:

shmall = (no. of postgresql servers) * (shmmax/4096)

If there are other daemons on the box that need to use shared memory,
then add their likely requirements to shmall too!

cheers

Mark