Re: hashjoins vs. Bloom filters (yet again)

On Wed, Aug 19, 2026 at 07:31:18PM +0200, Tomas Vondra wrote:
> On 8/19/26 17:05, Bruce Momjian wrote:
> > One topic that came up in the Pittsburgh AI Workshop was the idea of
> > combining indexes. For example, right now, all indexes point to heap,
> > and we usually go from index to heap. We can combine indexes using
> > bitmap scans of heap tids. Would there be any value of improving our
> > ability to combine indexes beyond bitmap scans?
> >
>
> Are you describing something like this [1]? That is, ability to build a
> bitmap (from bitmap index scan), and pass it into an index scan, so that
> it can benefit from the selective bitmap filter and ordering of the
> regular index scan?
>
> I think that's an interesting idea / scan variant, skipping a possibly
> expensive Sort. But I don't quite see how is that related to the topic
> of this thread? It transfers predicate within a single scan (from one
> index to the other), while the hashjoin bloom pushdown "transfers"
> predicates between different plan nodes, possibly very distant.

Yeah, not sure what I am asking. It was just a thought that maybe more
flexible index combining can be helpful.

--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EDB https://enterprisedb.com

Do not let urgent matters crowd out time for investment in the future.