Re: Tuning for PostGreSQL Database

From: Christopher Weimann (csw_at_k12hq.com)
Date: 07/24/03

  • Next message: Petri Helenius: "cpu performance counters" 
    Date: Thu, 24 Jul 2003 13:39:10 -0400
To: Terry Lambert <tlambert2@mindspring.com>

    On Wed 07/23/2003-11:55:25PM -0700, Terry Lambert wrote:
    >
    > > The question I have is: can pages in the inactive queue be used as disk
    > > cache?
    >
    > The answer is "yes, they can be reactivated and written to before
    > they are flushed if soft updates is enabled" and "yes, they can be
    > reactivated and read (but not written) to before they are flushed
    > if soft updates is not enabled".
    >
    > In general, this only happens for data pages, which is to say, the
    > pages containing user file data. Pages containing FS metadata are
    > specifically considered as "write through" or "virtually write
    > through".
    >
    > It doesn't happen for data pages, if they are explicitly fsync'ed
    > to ensure write ordering is guaranteed.
    >

    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 :)

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