Re: Tuning for PostGreSQL Database

From: Tom Samplonius (tom_at_sdf.com)
Date: 07/25/03

  • Next message: Christopher Weimann: "Re: Tuning for PostGreSQL Database" 
    Date: Fri, 25 Jul 2003 00:03:32 -0700 (PDT)
To: Christopher Weimann <csw@k12hq.com>

    On Thu, 24 Jul 2003, Christopher Weimann wrote:

    ...
    > So if PostGreSQL uses fsync when writing ( which I think is only true
    > on the write-ahead logs at this point ) that data will NOT wind up in
    > the cache. Anything that PostGreSQL reads should wind up in the cache?
    >
    > #uname -r
    > 4.7-RELEASE-p3
    >
    > # top -b | head -5
    > last pid: 58622; load averages: 1.96, 1.67, 1.47 up 2+12:59:15 13:31:39
    > 130 processes: 6 running, 124 sleeping
    >
    > Mem: 348M Active, 2628M Inact, 438M Wired, 155M Cache, 380M Buf, 76M Free
    > Swap: 4096M Total, 28K Used, 4096M Free
    >
    > The 2628M Inact is likley to be acting as cache?
    >
    > Basically I should stop worrying about this :)

      Maybe you should continue to worry. PostgreSQL isn't MySQL (or a
    typical server application). It reads all database pages into its shared
    memory area. It is wasteful for the DBMS and the OS to both cache this
    data. You'll want the PostgreSQL shared memory size to be around 75% the
    size of RAM (on a dedicated DBMS server). In fact, many commercial DBMS
    systems will use raw writes to bypass the OS cache!

    Tom

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