Re: Table AM Interface Enhancements

Hi, Alexander!

The revised rest of the patchset is attached.
> 0001 (was 0006) – I prefer the definition of AcquireSampleRowsFunc to
> stay in vacuum.h. If we move it to sampling.h then we would have to
> add there includes to define Relation, HeapTuple etc. I'd like to
> avoid this kind of change. Also, I've deleted
> table_beginscan_analyze(), because it's only called from
> tableam-specific AcquireSampleRowsFunc. Also I put some comments to
> heapam_scan_analyze_next_block() and heapam_scan_analyze_next_tuple()
> given that there are now no relevant comments for them in tableam.h.
> I've removed some redundancies from acquire_sample_rows(). And added
> comments to AcquireSampleRowsFunc based on what we have in FDW docs
> for this function. Did some small edits as well. As you suggested,
> turned back declarations for acquire_sample_rows() and compare_rows().
>

In my comment in the thread I was not thinking about returning the old name
acquire_sample_rows(), it was only about the declarations and the order of
functions to be one code block. To me heapam_acquire_sample_rows() looks
better for a name of heap implementation of *AcquireSampleRowsFunc(). I
suggest returning the name heapam_acquire_sample_rows() from v4. Sorry for
the confusion in this.

The changed type of static function that always returned true for heap
looks good to me:
static void heapam_scan_analyze_next_block

The same is for removing the comparison of always true "block_accepted" in
(heapam_)acquire_sample_rows()

Removing table_beginscan_analyze and call scan_begin() is not in the same
style as other table_beginscan_* functions. Though this is not a change in
functionality, I'd leave this part as it was in v4. Also, a comment about
it was introduced in v5:

src/backend/access/heap/heapam_handler.c: * with table_beginscan_analyze()

For comments I'd propose:
%s/In addition, store estimates/In addition, a function should store
estimates/g
%s/zerp/zero/g

> 0002 (was 0007) – I've turned the redundant "if", which you've pointed
> out, into an assert. Also, added some comments, most notably comment
> for TableAmRoutine.reloptions based on the indexam docs.
>

%s/validate sthe/validates the/g

This seems not needed, it's already inited to InvalidOid before.
+else
+accessMethod = default_table_access_method;

+ accessMethodId = InvalidOid;

This code came from 374c7a22904. I don't insist on this simplification in a
patch 0002.

Overall both patches look good to me.

Regards,
Pavel Borisov.