Re: Low Performance for big hospital server ..

William Yu wrote:

> Dave Cramer wrote:
>
>>
>>
>> William Yu wrote:
>>
>>> amrit@health2.moph.go.th wrote:
>>>
>>>> I will try to reduce shared buffer to 1536 [1.87 Mb].
>>>
>>>
>>>
>>>
>>> 1536 is probaby too low. I've tested a bunch of different settings
>>> on my  8GB Opteron server and 10K seems to be the best setting.
>>
>>
>>
>> Be careful here, he is not using opterons which can access physical
>> memory above 4G efficiently. Also he only has 4G the 6-10% rule still
>> applies
>
>
> 10% of 4GB is 400MB. 10K buffers is 80MB. Easily less than the 6-10%
> rule.
>
Correct, I didn't actually do the math, I refrain from giving actual
numbers as every system is different.

>
>>> To figure out your effective cache size, run top and add free+cached.
>>
>>
>>
>> My understanding is that effective cache is the sum of shared
>> buffers, plus kernel buffers, not sure what free + cached gives you?
>
>
> Not true. Effective cache size is the free memory available that the
> OS can use for caching for Postgres. In a system that runs nothing but
> Postgres, it's free + cached.

You still need to add in the shared buffers as they are part of the
"effective cache"

Dave

>
> ---------------------------(end of broadcast)---------------------------
> TIP 8: explain analyze is your friend
>
>

--
Dave Cramer
http://www.postgresintl.com
519 939 0336
ICQ#14675561