Horton

Re: BitmapHeapScan streaming read user and prelim refactoring

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Melanie Plageman <melanieplageman@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: 2024-03-29T23:56:39Z
Lists: pgsql-hackers 
On Sat, Mar 30, 2024 at 12:40 PM Tomas Vondra
<tomas.vondra@enterprisedb.com> wrote:
> Sorry, I meant the prefetch (readahead) built into ZFS. I may be wrong
> but I don't think the regular RA (in linux kernel) works for ZFS, right?

Right, it separate page cache ("ARC") and prefetch settings:

https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/Module%20Parameters.html

That's probably why Linux posix_fadvise didn't affect it, well that
and the fact, at a wild guess, that Solaris didn't have that system
call...

> I was wondering if we could use this (posix_fadvise) to improve that,
> essentially by issuing fadvise even for sequential patterns. But now
> that I think about that, if posix_fadvise works since 2.2, maybe RA
> works too now?)

It should work fine.  I am planning to look into this a bit some day
soon -- I think there may be some interesting interactions between
systems with big pages/records like ZFS/BTRFS/... and io_combine_limit
that might offer interesting optimisation tweak opportunities, but
first things first...

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.