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: Andres Freund <andres@anarazel.de>, Pg Hackers <pgsql-hackers@postgresql.org>, Thomas Munro <thomas.munro@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>, Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: 2024-02-27T01:50:28Z
Lists: pgsql-hackers

Attachments

On Fri, Feb 16, 2024 at 12:35:59PM -0500, Melanie Plageman wrote:
> In the attached v3, I've reordered the commits, updated some errant
> comments, and improved the commit messages.
> 
> I've also made some updates to the TIDBitmap API that seem like a
> clarity improvement to the API in general. These also reduce the diff
> for GIN when separating the TBMIterateResult from the
> TBM[Shared]Iterator. And these TIDBitmap API changes are now all in
> their own commits (previously those were in the same commit as adding
> the BitmapHeapScan streaming read user).
> 
> The three outstanding issues I see in the patch set are:
> 1) the lossy and exact page counters issue described in my previous
> email

I've resolved this. I added a new patch to the set which starts counting
even pages with no visible tuples toward lossy and exact pages. After an
off-list conversation with Andres, it seems that this omission in master
may not have been intentional.

Once we have only two types of pages to differentiate between (lossy and
exact [no longer have to care about "has no visible tuples"]), it is
easy enough to pass a "lossy" boolean paramater to
table_scan_bitmap_next_block(). I've done this in the attached v4.

- 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.