Re: Adding skip scan (including MDAM style range skip scan) to nbtree

On Mon, May 12, 2025 at 8:58 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> I wonder if we can fix this problem by getting rid of the old support
> routine #5, "options". It currently doesn't do anything, and I always
> thought it was strange that it was added "for uniformity" with other
> index AMs.

Attached patch completely removes the nbtree "options" support
function, while changing the support function number of skip support:
it becomes support function #5 (the number previously used by
"options"). This patch should fix the regression that Tomas complained
about in an expedient way.

It's likely that somebody else will run into the same problem in the
future, the next time that a new support function is needed. But I
think that it makes sense to do this much now -- we need a short term
solution for Postgres 18. Usually I would never suggest breaking
compatibility like this, but, remarkably, we have never actually done
anything with our current support function 5. It's not possible to
break compatibility with code that can never be called in the first
place, so I see no compatibility to preserve.

Questions for Alexander about the "options" support function:

* Why did you invent the whole idea of an "options" support function,
given that it doesn't actually do anything? I get that it might be a
good idea to add these kinds of functions in the future, but why
didn't you wait until nbtree *actually had a use* for them?

* I've removed some of the tests that you added, that (for whatever
reason) cover nbtree specifically. The test from alter_generic.sql.
There might be some kind of loss of test coverage. What do you think?

--
Peter Geoghegan