Horton

Re: Table AM Interface Enhancements

Nazir Bilal Yavuz <byavuz81@gmail.com>

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From: Nazir Bilal Yavuz <byavuz81@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Alexander Korotkov <aekorotkov@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>, Andres Freund <andres@anarazel.de>, Pavel Borisov <pashkin.elfe@gmail.com>, Japin Li <japinli@hotmail.com>, Mark Dilger <mark.dilger@enterprisedb.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Michael Paquier <michael@paquier.xyz>, Heikki Linnakangas <hlinnaka@iki.fi>, Thomas Munro <thomas.munro@gmail.com>
Date: 2024-04-15T16:41:19Z
Lists: pgsql-hackers 
Hi,

On Mon, 15 Apr 2024 at 18:36, Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Sat, Apr 13, 2024 at 5:28 AM Alexander Korotkov <aekorotkov@gmail.com> wrote:
> > Yes, I think so.  Table AM API deals with TIDs and block numbers, but
> > doesn't force on what they actually mean.  For example, in ZedStore
> > [1], data is stored on per-column B-trees, where TID used in table AM
> > is just a logical key of that B-trees.  Similarly, blockNumber is a
> > range for B-trees.
> >
> > c6fc50cb4028 and 041b96802ef are putting to acquire_sample_rows() an
> > assumption that we are sampling physical blocks as they are stored in
> > data files.  That couldn't anymore be some "logical" block numbers
> > with meaning only table AM implementation knows.  That was pointed out
> > by Andres [2].  I'm not sure if ZedStore is alive, but there could be
> > other table AM implementations like this, or other implementations in
> > development, etc.  Anyway, I don't feel good about narrowing the API,
> > which is there from pg12.
>
> I spent some time looking at this. I think it's valid to complain
> about the tighter coupling, but c6fc50cb4028 is there starting in v14,
> so I don't think I understand why the situation after 041b96802ef is
> materially worse than what we've had for the last few releases. I
> think it is worse in the sense that, before, you could dodge the
> problem without defining USE_PREFETCH, and now you can't, but I don't
> think we can regard nonphysical block numbers as a supported scenario
> on that basis.

I agree with you but I did not understand one thing. If out-of-core
AMs are used, does not all block sampling logic (BlockSampler_Init(),
BlockSampler_Next() etc.) need to be edited as well since these
functions assume block numbers are actual physical on-disk location,
right? I mean if the block number is something different than the
actual physical on-disk location, the acquire_sample_rows() function
looks wrong to me before c6fc50cb4028 as well.

-- 
Regards,
Nazir Bilal Yavuz
Microsoft

Commits

  1. Remove extra comment at TableAmRoutine.scan_analyze_next_block

  2. revert: Generalize relation analyze in table AM interface

  3. Revert: Allow table AM to store complex data structures in rd_amcache

  4. Revert: Allow table AM tuple_insert() method to return the different slot

  5. Revert: Allow locking updated tuples in tuple_update() and tuple_delete()

  6. Revert: Let table AM insertion methods control index insertion

  7. Revert: Custom reloptions for table AM

  8. Provide a way block-level table AMs could re-use acquire_sample_rows()

  9. Custom reloptions for table AM

  10. Use streaming I/O in ANALYZE.

  11. Revert "Custom reloptions for table AM"

  12. Let table AM insertion methods control index insertion

  13. Generalize relation analyze in table AM interface

  14. Improve error message for tts_(virtual|minimal)_is_current_xact_tuple

  15. Add comments on some MinimalTupleSlots methods usage

  16. Add TupleTableSlotOps.is_current_xact_tuple() method

  17. Allow table AM tuple_insert() method to return the different slot

  18. Allow table AM to store complex data structures in rd_amcache