Re: Table AM Interface Enhancements

On Tue, 16 Apr 2024 at 14:52, Alexander Korotkov <aekorotkov(at)gmail(dot)com>
wrote:

> On Mon, Apr 15, 2024 at 11:17 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > On 2024-04-15 16:02:00 -0400, Robert Haas wrote:
> > > Do you want that patch applied, not applied, or applied with some set
> of
> > > modifications?
> >
> > I think we should apply Alexander's proposed revert and then separately
> > discuss what we should do about 041b96802ef.
>
> Taking a closer look at acquire_sample_rows(), I think it would be
> good if table AM implementation would care about block-level (or
> whatever-level) sampling. So that acquire_sample_rows() just fetches
> tuples one-by-one from table AM implementation without any care about
> blocks. Possible table_beginscan_analyze() could take an argument of
> target number of tuples, then those tuples are just fetches with
> table_scan_analyze_next_tuple(). What do you think?
>
Hi, Alexander!

I like the idea of splitting abstraction levels for:
1. acquirefuncs (FDW or physical table)
2. new specific row fetch functions (alike to existing
_scan_analyze_next_tuple()), that could be AM-specific.

Then scan_analyze_next_block() or another iteration algorithm would be
contained inside table AM implementation of _scan_analyze_next_tuple().

So, init of scan state would be inside table AM implementation of
_beginscan_analyze(). Scan state (like BlockSamplerData or other state that
could be custom for AM) could be transferred from _beginscan_analyze() to
_scan_analyze_next_tuple() by some opaque AM-specific data structure. If so
we'll also may need AM-specific table_endscan_analyze to clean it.

Regards,
Pavel