Horton

Re: BitmapHeapScan streaming read user and prelim refactoring

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: Tomas Vondra <tomas.vondra@enterprisedb.com>, Michael Paquier <michael@paquier.xyz>, Thomas Munro <thomas.munro@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: 2024-04-25T23:28:45Z
Lists: pgsql-hackers 
Melanie Plageman <melanieplageman@gmail.com> writes:
> On Wed, Apr 24, 2024 at 4:46 PM Melanie Plageman
> <melanieplageman@gmail.com> wrote:
>> After thinking about it more, I suppose we can't add a test that
>> relies on the relation being all visible in the VM in a group in the
>> parallel schedule. I'm not sure this edge case is important enough to
>> merit its own group or an isolation test. What do you think?

> Andres rightly pointed out to me off-list that if I just used a temp
> table, the table would only be visible to the testing backend anyway.
> I've done that in the attached v2. Now the test is deterministic.

Hmm, is that actually true?  There's no more reason to think a tuple
in a temp table is old enough to be visible to all other sessions
than one in any other table.  It could be all right if we had a
special-case rule for setting all-visible in temp tables.  Which
indeed I thought we had, but I can't find any evidence of that in
vacuumlazy.c, nor did a trawl of the commit log turn up anything
promising.  Am I just looking in the wrong place?

			regards, tom lane

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.