Re: Tuning for PostGreSQL Database

From: Simon J Mudd (sjmudd_at_pobox.com)
Date: 07/22/03

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    To: freebsd-performance@freebsd.org
Date: 22 Jul 2003 20:05:53 +0200

    jim@nasby.net ("Jim C. Nasby") writes:

    > > On Sat, 19 Jul 2003, Tom Samplonius wrote:
    > > > Softupdates on, async off. Softupdates is just a better async.
    > >
    > > postgresql fsync's all its files before returning from a commit in order
    > > to ensure durability, right? Does softupdates interfere with the
    > > functioning of sync(2)/fsync(2)?
    >
    > No, afaik it only fsync's the write-ahead-logs.

    Someone else mentioned Qmail. I use Postfix and I know the author
    relies on fsync semantics before confirming the acceptance of email.
    I'm sure Qmail (and sendmail, ...) does the same. They should do -
    the RFC requires this (that mail can't be lost once it is accepted for
    delivery).

    Therefore I think we are confusing 2 different issues. The effect of
    soft-updates (which tries to reorder writes to ensure FS recover is
    easier) and sync/fsync which only returns when the FS or file have
    been flushed to disk.

    I would guess that PostGreSQL uses fsync() and softupdates do not
    effect the fsync() semantics.

    Or am I missing something?

    Simon

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