Re: [PERFORM] shared_buffers/effective_cache_size on 96GB server

[Julien Cigar]

On 10/10/2012 10:30, Strahinja Kustudić wrote:
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.


also with 15k SCSI you can reduce random_page_cost to 3.5 (instead of 4.0)
I also recommend to raise cpu_tuple_cost to 0.05 (instead of 0.01), set 
vm.swappiness to 0, vm.overcommit_memory to 2, and finally raise the 
read-ahead (something like 8192)

Strahinja Kustudić| System Engineer | Nordeus



On Wed, Oct 10, 2012 at 10:11 AM, Julien Cigar <jci...@ulb.ac.be 
<mailto:jci...@ulb.ac.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


    -- 
    No trees were killed in the creation of this message.
    However, many electrons were terribly inconvenienced.



    --
    Sent via pgsql-performance mailing list
    (pgsql-performance@postgresql.org
    <mailto:pgsql-performance@postgresql.org>)
    To make changes to your subscription:
    http://www.postgresql.org/mailpref/pgsql-performance




--
No trees were killed in the creation of this message.
However, many electrons were terribly inconvenienced.

<<attachment: jcigar.vcf>>-- 
Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance