Re: BitmapHeapScan streaming read user and prelim refactoring

On Sat, May 11, 2024 at 3:18 PM Tomas Vondra
<tomas(dot)vondra(at)enterprisedb(dot)com> wrote:
>
> On 5/10/24 21:48, Melanie Plageman wrote:
> > Attached is v3. I didn't use your exact language because the test
> > wouldn't actually verify that we properly discard the tuples. Whether
> > or not the empty tuples are all emitted, it just resets the counter to
> > 0. I decided to go with "exercise" instead.
> >
>
> I did go over the v3 patch, did a bunch of tests, and I think it's fine
> and ready to go. The one thing that might need some minor tweaks is the
> commit message.
>
> 1) Isn't the subject "Remove incorrect assert" a bit misleading, as the
> patch does not simply remove an assert, but replaces it with a reset of
> the field the assert used to check? (The commit message does not mention
> this either, at least not explicitly.)

I've updated the commit message.

> 2) The "heap AM-specific bitmap heap scan code" sounds a bit strange to
> me, isn't the first "heap" unnecessary?

bitmap heap scan has been used to refer to bitmap table scans, as the
name wasn't changed from heap when the table AM API was added (e.g.
BitmapHeapNext() is used by all table AMs doing bitmap table scans).
04e72ed617be specifically pushed the skip fetch optimization into heap
implementations of bitmap table scan callbacks, so it was important to
make this distinction. I've changed the commit message to say heap AM
implementations of bitmap table scan callbacks.

While looking at the patch again, I wondered if I should set
enable_material=false in the test. It doesn't matter from the
perspective of exercising the correct code; however, I wasn't sure if
disabling materialization would make the test more resilient against
future planner changes which could cause it to incorrectly fail.

- Melanie