On Mon, May 5, 2025 at 10:14:22PM +1200, David Rowley wrote:
> On Fri, 2 May 2025 at 14:44, Bruce Momjian <bruce@momjian.us> wrote:
> > You can see the most current HTML-built version here:
> >
> > https://momjian.us/pgsql_docs/release-18.html
>
> Thanks for working on these.
>
> For "Improve the performance of hash joins (David Rowley)", 0f5738202
> did the same thing for GROUP BY and hashed subplans too. It might be
> worth adjusting this to some more generic text which covers all of
> these. Something like "Speed up hash value generation in Hash Join,
> GROUP BY, hashed Subplan and hashed set operations</p><p>This change
> also allows JIT compilation for obtaining hash values for these
> operations". The set operations I likely should have mentioned in the
> commit message.
Okay, text added.
> There's also Jeff's work in cc721c459, 4d143509c, a0942f441, 626df47ad
> which does work to reduce the memory overheads of hashed GROUP BY,
> hashed Subplans and hashed set operations. I think Jeff might have
> understated the possible performance gains from these commits. I very
> much think this is worth something like "Reduce memory overheads for
> hashed GROUP BY, subplans and set operation processing (Jeff Davis)".
>
> A quick test with: explain analyze select a from
> generate_series(1,1000000) a group by a;
>
> v17: Batches: 1 Memory Usage: 90145kB
> v18: Batches: 1 Memory Usage: 57385kB
>
> A 37% reduction for this case. Not insignificant.
Commits added and Jeff's name added, patch attached.
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EDB https://enterprisedb.com
Do not let urgent matters crowd out time for investment in the future.
