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: Melanie Plageman <melanieplageman@gmail.com>
Cc: Tomas Vondra <tv@fuzzy.cz>, Heikki Linnakangas <hlinnaka@iki.fi>, Andres Freund <andres@anarazel.de>, Pg Hackers <pgsql-hackers@postgresql.org>, Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: 2024-10-08T20:56:05Z
Lists: pgsql-hackers 
On Sat, Sep 28, 2024 at 8:13 AM Melanie Plageman
<melanieplageman@gmail.com> wrote:
> For the top-level TableScanDescData, I suggest we use a union with the
> members of each scan type in it in anonymous structs (see 0001).

Just by the way, you can't use anonymous structs or unions in C99
(that was added to C11), but most compilers accept them silently
unless you use eg -std=c99.  Some buildfarm animal or other would
bleat about that (ask me how I know), but out CI doesn't pick it up
:-(  Maybe we should fix that.  That's why you see a lot of code
around that accesses unions through a member with a name like "u",
because the author was shaking her fist at the god of standards and
steadfastly refusing to think of a name.  It's a shame in cases where
you want to retrofit a union into existing code without having to
adjust the code that accesses one of the members...

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.