Horton

Re: BitmapHeapScan streaming read user and prelim refactoring

Richard Guo <guofenglinux@gmail.com>

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From: Richard Guo <guofenglinux@gmail.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Melanie Plageman <melanieplageman@gmail.com>, 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: 2024-04-12T03:18:06Z
Lists: pgsql-hackers 
On Sun, Apr 7, 2024 at 10:42 PM Tomas Vondra <tomas.vondra@enterprisedb.com>
wrote:

> create table t (a int, b int) with (fillfactor=10);
> insert into t select mod((i/22),2), (i/22) from generate_series(0,1000)
> S(i);
> create index on t(a);
> vacuum analyze t;
>
> set enable_indexonlyscan = off;
> set enable_seqscan = off;
> explain (analyze, verbose) select 1 from (values (1)) s(x) where exists
> (select * from t where a = x);
>
> KABOOM!


FWIW, it seems to me that this assert could be triggered in cases where,
during a join, not all inner tuples need to be scanned before skipping to
next outer tuple.  This can happen for 'single_match' or anti-join.

The query provided by Tomas is an example of 'single_match' case.  Here
is a query for anti-join that can also trigger this assert.

explain (analyze, verbose)
select t1.a from t t1 left join t t2 on t2.a = 1 where t2.a is null;
server closed the connection unexpectedly

Thanks
Richard

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.