Horton

Re: BitmapHeapScan streaming read user and prelim refactoring

Tomas Vondra <tomas.vondra@enterprisedb.com>

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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>, Dilip Kumar <dilipbalaut@gmail.com>, Melanie Plageman <melanieplageman@gmail.com>
Cc: Nazir Bilal Yavuz <byavuz81@gmail.com>, Andres Freund <andres@anarazel.de>, Pg Hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2024-03-13T18:14:36Z
Lists: pgsql-hackers 
On 3/13/24 14:34, Heikki Linnakangas wrote:
> ...
> 
> Lots of discussion happening on the performance results but it seems
> that there is no performance impact with the preliminary patches up to
> v5-0013-Streaming-Read-API.patch. I'm focusing purely on those
> preliminary patches now, because I think they're worthwhile cleanups
> independent of the streaming read API.
> 

Not quite true - the comparison I shared on 29/2 [1] shows a serious
regression caused by the 0010 patch. We've been investigating this with
Melanie off list, but we don't have any clear findings yet (except that
it's clearly due to moving BitmapAdjustPrefetchIterator() a bit down.

But if we revert this (and move the BitmapAdjustPrefetchIterator back),
the regression should disappear, and we can merge these preparatory
patches. We'll have to deal with the regression (or something very
similar) when merging the remaining patches.

regards


[1]
https://www.postgresql.org/message-id/91090d58-7d3f-4447-9425-f24ba66e292a%40enterprisedb.com
-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.