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: Andres Freund <andres@anarazel.de>, Pg Hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: 2024-02-28T20:06:08Z
Lists: pgsql-hackers 
On Wed, Feb 28, 2024 at 2:23 PM Tomas Vondra
<tomas.vondra@enterprisedb.com> wrote:
>
> On 2/28/24 15:56, Tomas Vondra wrote:
> >> ...
> >
> > Sure, I can do that. It'll take a couple hours to get the results, I'll
> > share them when I have them.
> >
>
> Here are the results with only patches 0001 - 0012 applied (i.e. without
> the patch introducing the streaming read API, and the patch switching
> the bitmap heap scan to use it).
>
> The changes in performance don't disappear entirely, but the scale is
> certainly much smaller - both in the complete results for all runs, and
> for the "optimal" runs that would actually pick bitmapscan.

Hmm. I'm trying to think how my refactor could have had this impact.
It seems like all the most notable regressions are with 4 parallel
workers. What do the numeric column labels mean across the top
(2,4,8,16...) -- are they related to "matches"? And if so, what does
that mean?

- 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.