Re: Hash index todo list item

On Thu, Sep 06, 2007 at 11:56:25PM -0700, Neil Conway wrote:
> On Sun, 2007-02-09 at 13:04 -0500, Kenneth Marshall wrote:
> > 2. Evaluate the performance of different hash index implementations
> > and/or changes to the current implementation. My current plan is
> > to keep the implementation as simple as possible and still provide
> > the desired performance. Several hash index suggestions deal with
> > changing the layout of the keys on a page to improve lookup
> > performance, including reducing the bucket size to a fraction of
> > a page or only storing the hash value on the page, instead of
> > the index value itself.
>
> You might find this patch useful:
>
> http://archives.postgresql.org/pgsql-patches/2005-05/msg00164.php
>
> It implements the "just store the hash in the index" idea; it also sorts
> the entries in a bucket by the hash value, which allows binary search to
> be used to locate candidate matches.
>
> I was surprised that this didn't result in a performance improvement for
> the benchmarks that I ran, but I never got around to investigating
> further (either running more benchmarks or checking whether there was a
> bug in the implementation).
>
> Unfortunately, the patch doesn't apply cleanly to HEAD, but I can merge
> it up to HEAD if you'd like.
>
> -Neil
>
I have another question. Did the scan code at this time use the
heap-order scanning? Could that have had an impact on the patch
performance?

Ken