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: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Tomas Vondra <tomas@vondra.me>, Heikki Linnakangas <hlinnaka@iki.fi>, Thomas Munro <thomas.munro@gmail.com>, Andres Freund <andres@anarazel.de>, Pg Hackers <pgsql-hackers@postgresql.org>, Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: 2025-01-22T21:24:19Z
Lists: pgsql-hackers

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On Mon, Dec 9, 2024 at 1:22 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> Are we planning to commit this refactoring? I think this refactoring
> makes the overall code of BitmapHeapNext() quite clean and readable.
> I haven't read all patches but 0001-0006 including 0009 makes this
> code quite clean and readable. I like the refactoring of merging of
> the shared iterator and the private iterator also.

Thanks for the feedback, Dilip. I've pushed the patches through 0006.

I've reorganized the remaining patches in attached v26.

0001 is just the refactoring to push the setup into a helper.
0002-0003 are required refactoring of the TBMIterateResult and
TBMIterator to support the read stream API.
0004 implements using the read stream API and removing the old prefetching code.
0005 removes the table_scan_bitmap_next_block() callback, as it is not
really used anymore in BitmapHeapNext() to get the next block.

I could use review feedback on all of them. 0001 should be ready to
push once I get some review.

0002 and 0003 shouldn't be committed without committing the read
stream commit because they are not improvements on their own. However,
I have an outstanding question in 0003 that I could use input on.

0004 needs another round of benchmarking.

0005 needs review once the others are dealt with.

- 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.