Re: index prefetching

On Wed, Dec 10, 2025 at 9:21 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> Attached is v4.

Attached is v5. Changes from v4:

* Simplified and optimized index-only scans, with a particular
emphasis on avoiding regressions with nested loop joins with an inner
index-only scan.

There were quite a number of small problems/dead code related to
index-only scans fixed by this new v5. Overall, I'm quite a bit
happier with the state of index-only scans, which I'd not paid too
much attention to before now.

* Added Valgrind instrumentation to the hash index patch, which was
required to fix some false positives.

The generic indexam_util_batch_unlock routine had Valgrind
instrumentation in earlier versions, just to keep nbtree's buffer
locking checks from generating similar false positives. Some time
later, when I added the hashgetbatch patch, there were new Valgrind
false positives during hash index scans -- which I missed at first.
This new v5 revisions adds similar Valgrind checks to hash itself
(changes that add code that is more or less a direct port of the stuff
added to nbtree by commit 4a70f829), which fixes the false positives,
and is independently useful.

The rule for amgetbatch-based index AMs is that they must have similar
buffer locking instrumentation. That seems like a good thing.

--
Peter Geoghegan