Horton

Re: BitmapHeapScan streaming read user and prelim refactoring

Tomas Vondra <tomas.vondra@enterprisedb.com>

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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Melanie Plageman <melanieplageman@gmail.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: 2024-05-14T18:44:45Z
Lists: pgsql-hackers 
On 5/14/24 20:40, Melanie Plageman wrote:
> On Tue, May 14, 2024 at 2:33 PM Tomas Vondra
> <tomas.vondra@enterprisedb.com> wrote:
>>
>> On 5/14/24 19:42, Melanie Plageman wrote:
>>> I've fixed this. I've also set enable_material off as I mentioned I
>>> might in my earlier mail.
>>>
>>
>> I'm not sure this (setting more and more GUCs to prevent hypothetical
>> plan changes) is a good practice. Because how do you know the plan does
>> not change for some other unexpected reason, possibly in the future?
> 
> Sure. So, you think it is better not to have enable_material = false?
> 

Right. Unless it's actually needed to force the necessary plan.

>> IMHO if the test requires a specific plan, it's better to do an actual
>> "explain (rows off, costs off)" to check that.
> 
> When you say "rows off", do you mean do something to ensure that it
> doesn't return tuples? Because I don't see a ROWS option for EXPLAIN
> in the docs.
> 

Sorry, I meant to hide the cardinality estimates in the explain, but I
got confused. "COSTS OFF" is enough.


regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.