Re: Bitmap index scan preread using posix_fadvise (Was: There's random access and then there's random access)

Nice!

- Luke

On 1/30/08 9:22 AM, "Gregory Stark" <stark(at)enterprisedb(dot)com> wrote:

>
> Here's the WIP patch for doing prereading when doing bitmap index scans.
>
> I was performance testing it as I was developing it here:
>
> http://archives.postgresql.org/pgsql-hackers/2007-12/msg00395.php
>
> Note that this only kicks in for bitmap index scans which are kind of tricky
> to generate. I used the attached function to generate them in the post above.
>
> Also note I wouldn't expect to see much benefit unless you're on a raid array,
> even a small one. But if you are on a raid array then the benefit should be
> immediately obvious or else posix_fadvise just isn't working for you. I would
> be interested in hearing on which OSes it does or doesn't work.
>
> *If* this is the approach we want to take rather than restructure the buffer
> manager to avoid taking two trips by marking the buffer i/o-in-progress and
> saving the pinned buffer in the bitmap heap scan then this is more or less in
> final form. Aside from some autoconf tests and the documentation for the GUC I
> think it's all in there.
>
>