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: 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: 2024-04-25T23:03:57Z
Lists: pgsql-hackers

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On Wed, Apr 24, 2024 at 4:46 PM Melanie Plageman
<melanieplageman@gmail.com> wrote:
>
> On Tue, Apr 23, 2024 at 6:43 PM Tomas Vondra
> <tomas.vondra@enterprisedb.com> wrote:
> >
> > On 4/23/24 18:05, Melanie Plageman wrote:
> > > One other note: there is some concurrency effect in the parallel
> > > schedule group containing "join" where you won't trip the assert if
> > > all the tests in that group in the parallel schedule are run. But, if
> > > you would like to verify that the test exercises the correct code,
> > > just reduce the group containing "join".
> > >
> >
> > That is ... interesting. Doesn't that mean that most test runs won't
> > actually detect the problem? That would make the test a bit useless.
>
> Yes, I should really have thought about it more. After further
> investigation, I found that the reason it doesn't trip the assert when
> the join test is run concurrently with other tests is that the SELECT
> query doesn't use the skip fetch optimization because the VACUUM
> doesn't set the pages all visible in the VM. In this case, it's
> because the tuples' xmins are not before VacuumCutoffs->OldestXmin
> (which is derived from GetOldestNonRemovableTransactionId()).
>
> 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.

- 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.