Horton

Re: BitmapHeapScan streaming read user and prelim refactoring

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Melanie Plageman <melanieplageman@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: 2024-03-29T13:36:08Z
Lists: pgsql-hackers 
On Sat, Mar 30, 2024 at 12:17 AM Thomas Munro <thomas.munro@gmail.com> wrote:
> eic unpatched patched
> 0        4172    9572
> 1       30846   10376
> 2       18435    5562
> 4       18980    3503
> 8       18980    2680
> 16      18976    3233

... but the patched version gets down to a low number for eic=0 too if
you turn up the blockdev --setra so that it also gets Linux RA
treatment, making it the clear winner on all eic settings.  Patched
doesn't improve.  So, for low IOPS storage at least, when you're on
the borderline between random and sequential, ie bitmap with a lot of
1s in it, it seems there are cases where patched doesn't trigger Linux
RA but unpatched does, and you can tune your way out of that, and then
there are cases where the IOPS limit is reached due to small reads,
but patched does better because of larger I/Os that are likely under
the same circumstances.  Does that make sense?

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.