Thread: O_DIRECT option used?

O_DIRECT option used?

From
Ruslan A Dautkhanov
Date:
Hello,

        In the FreeBSD 4.5 appear additional O_DIRECT option for open(2),
    which mean "eliminate or reduce cache effects". I think, that double
    buffering the same disk blocks is ineffective. I grepped all
    PostgreSQL sources for this options and didn't find this anywhere.
    PgSQL have it's own disk caches, which should be smart
    (DB can know what data should be cached first better than OS).
    Why wasting OS memory for double caches? OS can use this caches
    for other disk blocks, so total cached disk blocks in whole
    system will be much bigger. If you have no plans to implement this,
    please let us know what source files I should looking for patching.
    I think it's somewhere DB tables files are opened (and maybe
    WAL files too).   Thanks a lot on any comments.



    ---
     best regards,
    Ruslan A Dautkhanov   rusland@scn.ru

Re: O_DIRECT option used?

From
Bruce Momjian
Date:
Read the developer's FAQ on advanced features.  We don't think it will
be a big win.

---------------------------------------------------------------------------

Ruslan A Dautkhanov wrote:
>             Hello,
>
>         In the FreeBSD 4.5 appear additional O_DIRECT option for open(2),
>     which mean "eliminate or reduce cache effects". I think, that double
>     buffering the same disk blocks is ineffective. I grepped all
>     PostgreSQL sources for this options and didn't find this anywhere.
>     PgSQL have it's own disk caches, which should be smart
>     (DB can know what data should be cached first better than OS).
>     Why wasting OS memory for double caches? OS can use this caches
>     for other disk blocks, so total cached disk blocks in whole
>     system will be much bigger. If you have no plans to implement this,
>     please let us know what source files I should looking for patching.
>     I think it's somewhere DB tables files are opened (and maybe
>     WAL files too).   Thanks a lot on any comments.
>
>
>
>     ---
>      best regards,
>     Ruslan A Dautkhanov   rusland@scn.ru

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