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: Thomas Munro <thomas.munro@gmail.com>
Cc: Tomas Vondra <tomas@vondra.me>, Nazir Bilal Yavuz <byavuz81@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Andres Freund <andres@anarazel.de>, Pg Hackers <pgsql-hackers@postgresql.org>
Date: 2025-02-24T16:18:01Z
Lists: pgsql-hackers

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On Fri, Feb 21, 2025 at 5:00 PM Melanie Plageman
<melanieplageman@gmail.com> wrote:
>
> I thought about doing this, but in the end I decided against this
> approach. If we wanted to make it easy to palloc arrays of different
> sizes and have tbm_extract_page_tuple extract that many tuples into
> the array, we'd have to change more of the code anyway because
> tbm_extract_page_tuple is what tells us how many tuples there are to
> begin with. We could save this somewhere while filling in the
> PagetableEntries initially, but that is a bigger change.
>
> And, passing a length would also mean more callers would have to know
> about TBM_MAX_TUPLES_PER_PAGE, which I think is already kind of a hack
> since it is defined as MaxHeapTuplesPerPage.

I changed my mind. I think since the struct I added was only used for
tbm_extract_page_tuple(), it was a bit weird. I also think it is okay
for callers to use TBM_MAX_TUPLES_PER_PAGE. I ended up revising this
to use the same API you implemented for TIDStore in
TidStoreGetBlockOffsets(). The caller passes an array and the size of
the array and tbm_extract_page_tuple() fills in that many offsets and
returns the total number of offsets. It avoids adding a new struct and
means callers could pass a different value than
TBM_MAX_TUPLES_PER_PAGE. Overall, I like it.

- 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.