Horton

Re: BitmapHeapScan streaming read user and prelim refactoring

Melanie Plageman <melanieplageman@gmail.com>

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From: Melanie Plageman <melanieplageman@gmail.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Michael Paquier <michael@paquier.xyz>, Thomas Munro <thomas.munro@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Andres Freund <andres@anarazel.de>, Pg Hackers <pgsql-hackers@postgresql.org>, Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: 2024-05-13T14:05:03Z
Lists: pgsql-hackers

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On Sat, May 11, 2024 at 3:18 PM Tomas Vondra
<tomas.vondra@enterprisedb.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

Commits

  1. Fix bitmapheapscan incorrect recheck of NULL tuples

  2. Increase default maintenance_io_concurrency to 16

  3. Separate TBM[Shared|Private]Iterator and TBMIterateResult

  4. Improve read_stream.c advice for dense streams.

  5. Increase default effective_io_concurrency to 16

  6. Delay extraction of TIDBitmap per page offsets

  7. Add lossy indicator to TBMIterateResult

  8. Move BitmapTableScan per-scan setup into a helper

  9. Add and use BitmapHeapScanDescData struct

  10. Fix bitmap table scan crash on iterator release

  11. Bitmap Table Scans use unified TBMIterator

  12. Add common interface for TBMIterators

  13. Make table_scan_bitmap_next_block() async-friendly

  14. Move EXPLAIN counter increment to heapam_scan_bitmap_next_block

  15. Refactor tidstore.c iterator buffering.

  16. BitmapHeapScan: Remove incorrect assert and reset field

  17. Change BitmapAdjustPrefetchIterator to accept BlockNumber

  18. BitmapHeapScan: Use correct recheck flag for skip_fetch

  19. BitmapHeapScan: Push skip_fetch optimization into table AM

  20. BitmapHeapScan: postpone setting can_skip_fetch

  21. BitmapHeapScan: begin scan after bitmap creation

  22. Fix EXPLAIN Bitmap heap scan to count pages with no visible tuples

  23. Remove redundant snapshot copying from parallel leader to workers

  24. Remove some obsolete smgrcloseall() calls.

  25. Remove the "snapshot too old" feature.

  26. Compute XID horizon for page level index vacuum on primary.