Re: shared_buffers/effective_cache_size on 96GB server

Thanks for very fast replies everyone :)

@Laurenz I know that effective cache size is only used for the query
planner, what I was saying is that if I tell it that it can have 90GB
cached items, that is not trues, since the OS and Postgres process itself
can take more than 6GB, which would mean 90GB is not the correct value, but
if effective_cache size should be shared_buffers+page cache as Tomas said,
than 90GB, won't be a problem.

@Tomas here are the values:

# cat /proc/sys/vm/swappiness
60
# cat /proc/sys/vm/overcommit_memory
0
# cat /proc/sys/vm/overcommit_ratio
50

I will turn of swappiness, I was meaning to do that, but I don't know much
about the overcommit settings, I will read what they do.

@Julien thanks for the suggestions, I will tweak them like you suggested.

Strahinja Kustudić | System Engineer | Nordeus

On Wed, Oct 10, 2012 at 10:11 AM, Julien Cigar <jcigar(at)ulb(dot)ac(dot)be> wrote:

> On 10/10/2012 09:12, Strahinja Kustudić wrote:
>
>> Hi everyone,
>>
>
> Hello,
>
>
>
>> I have a Postgresql 9.1 dedicated server with 16 cores, 96GB RAM and
>> RAID10 15K SCSI drives which is runing Centos 6.2 x64. This server is
>> mainly used for inserting/updating large amounts of data via
>> copy/insert/update commands, and seldom for running select queries.
>>
>> Here are the relevant configuration parameters I changed:
>>
>> shared_buffers = 10GB
>>
>
> Generally going over 4GB for shared_buffers doesn't help.. some of the
> overhead of bgwriter and checkpoints is more or less linear in the size of
> shared_buffers ..
>
> effective_cache_size = 90GB
>>
>
> effective_cache_size should be ~75% of the RAM (if it's a dedicated server)
>
> work_mem = 32MB
>>
>
> with 96GB of RAM I would raise default work_mem to something like 128MB
>
> maintenance_work_mem = 512MB
>>
>
> again, with 96GB of ram you can raise maintenance_work_mem to something
> like 4GB
>
>
> checkpoint_segments = 64
>> checkpoint_completion_target = 0.8
>>
>> My biggest concern are shared_buffers and effective_cache_size, should I
>> increase shared_buffers and decrease effective_cache_size? I read that
>> values above 10GB for shared_buffers give lower performance, than smaller
>> amounts?
>>
>> free is currently reporting (during the loading of data):
>>
>> $ free -m
>> total used free shared buffers cached
>> Mem: 96730 96418 311 0 71 93120
>> -/+ buffers/cache: 3227 93502
>> Swap: 21000 51 20949
>>
>> So it did a little swapping, but only minor, still I should probably
>> decrease shared_buffers so there is no swapping at all.
>>
>> Thanks in advance,
>> Strahinja
>>
>
> Julien
>
>
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