Re: More shared_buffers instead of effective_cache_size?

On Thu, Sep 4, 2008 at 2:01 PM, Ulrich <ulrich(dot)mierendorff(at)gmx(dot)net> wrote:
> Scott Marlowe wrote:
>>
>> On Thu, Sep 4, 2008 at 1:39 PM, Ulrich <ulrich(dot)mierendorff(at)gmx(dot)net> wrote:
>>
>>>>
>>>> I wouldn't set shared_buffers that high
>>>> just because things like vacuum and sorts need memory too
>>>>
>>>
>>> Okay, I understand that vacuum uses memory, but I thought sorts are done
>>> in
>>> work_mem? I am only sorting the result of one query which will never
>>> return
>>> more than 500 rows.
>>>
>>
>> You can probably play with larger shared memory, but I'm betting that
>> the fact that you're running under a VM is gonna weigh eveything down
>> a great deal, to the point that you're tuning is going to have minimal
>> effect.
>>
>
> Hmm... Why do you think so? Is there a reason for it or do other people have
> problems with virtual servers and databases?
> I have reserved cpu power and reserved ram (okay, not much, but it is
> reserved ;-) ), the only thing I dont have is reserved file-cache.

Well, Databases tend to be IO bound, and VMs don't tend to focus on IO
performance as much as CPU/Memory performance. Also, things like
shared memory likely don't get as much attention in a VM either. Just
guessing, I haven't tested a lot of VMs.