Re: Table AM Interface Enhancements - Mailing list pgsql-hackers

From Pavel Borisov
Subject Re: Table AM Interface Enhancements
Date
Msg-id CALT9ZEGUscnS2nu6FssorVMq2hC5vzc6LuewWjMmA4insZBp2Q@mail.gmail.com
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In response to Re: Table AM Interface Enhancements  (Alexander Korotkov <aekorotkov@gmail.com>)
List pgsql-hackers


On Tue, 16 Apr 2024 at 14:52, Alexander Korotkov <aekorotkov@gmail.com> wrote:
On Mon, Apr 15, 2024 at 11:17 PM Andres Freund <andres@anarazel.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




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