Re: Tuning Effective Cache Question - Mailing list pgsql-performance

From Chris Hoover
Subject Re: Tuning Effective Cache Question
Date
Msg-id 1d219a6f050817101729be31a0@mail.gmail.com
Whole thread Raw
List pgsql-performance
Sorry, forgot to state that we are still on PG 7.3.4.

On 8/17/05, Chris Hoover <revoohc@gmail.com> wrote:
> I have some questions about tuning my effective_cache_size
>
> I have a RHEL 2.1 box running with dual Xeon (2.6 GHz I believe and
> they have HT on).  The box has 8GB memory.  In my postgresql.conf, I
> have set the effective_cache_size = 530505 (~4GB).
>
> However, I am noticing on this machine, top is telling me that I have
> ~3.5GB in the buff and only 3GB in cached.
>
> Here are the exact numbers:
> Mem:  7720040K av, 7714364K used,    5676K free,  314816K shrd, 3737540K buff
> Swap: 2096440K av,  119448K used, 1976992K free                 3188192K cached
>
>
> 1.  Is the configuration that linux is running in hurting PostgreSQL in any way?
>
> 2.  Is there a negative impact of the effective_cache_size being
> larger than the actual cached memory?
>
> 3.  What effect postive or negative does the buff memory have on PostgreSQL.\
>
> 4.  What exactly is this buff memory used for?  We have had a time
> trying to find a good explanation of what it means.
>
> Overall, this system appears to be running fine.  However, I was taken
> back when I saw the current memory configuration.  We have been
> walking a fine line performance wise, and can quickly become i/o
> starved.  So I want to make sure that I am not pushing the db towards
> the i/o starved side.
>
> Thanks for any insight,
>
> Chris
>

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