Horton

Re: Adding skip scan (including MDAM style range skip scan) to nbtree

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Tomas Vondra <tomas@vondra.me>
Cc: Mark Dilger <mark.dilger@enterprisedb.com>, Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers@lists.postgresql.org, Matthias van de Meent <boekewurm+postgres@gmail.com>
Date: 2025-05-09T13:33:11Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. nbtree: Always set skipScan flag on rescan.

  2. meson: Build numeric.c with -ftree-vectorize.

  3. Fix "variable not found in subplan target lists" in semijoin de-duplication.

  4. Revert "nbtree: Remove useless row compare arg."

  5. nbtree: Remove useless row compare arg.

  6. Prevent premature nbtree array advancement.

  7. nbtree: tighten up array recheck rules.

  8. Avoid treating nonrequired nbtree keys as required.

  9. Adjust overstrong nbtree skip array assertion.

  10. Make NULL tuple values always advance skip arrays.

  11. Avoid extra index searches through preprocessing.

  12. Improve nbtree skip scan primitive scan scheduling.

  13. Further optimize nbtree search scan key comparisons.

  14. Add nbtree skip scan optimization.

  15. Improve nbtree array primitive scan scheduling.

  16. nbtree: Make BTMaxItemSize into object-like macro.

  17. Show index search count in EXPLAIN ANALYZE, take 2.

  18. Make parallel nbtree index scans use an LWLock.

  19. Show index search count in EXPLAIN ANALYZE.

  20. Avoid nbtree parallel scan currPos confusion.

  21. nbtree: Remove useless 'strat' local variable.

  22. Normalize nbtree truncated high key array behavior.

  23. Refactor handling of nbtree array redundancies.

  24. Fix nbtree pgstats accounting with parallel scans.

  25. Avoid parallel nbtree index scan hangs with SAOPs.

  26. Show Parallel Bitmap Heap Scan worker stats in EXPLAIN ANALYZE

  27. Enhance nbtree ScalarArrayOp execution.

  28. Skip checking of scan keys required for directional scan in B-tree

  29. Instead of using a numberOfRequiredKeys count to distinguish required

On Fri, May 9, 2025 at 8:58 AM Tomas Vondra <tomas@vondra.me> wrote:
> My conclusion from this is that 92fe23d93aa ends up doing a lot of
> malloc calls, and this is what makes causes the regression. Otherwise
> setting the MALLOC_TOP_PAD_ would not help like this. But I haven't
> looked at the code, and I wouldn't have guessed the query to have
> anything to do with skip scan ...

While it's just about plausible that added nbtree preprocessing
allocation overhead could account for this, I don't think it's
actually possible here, since, as you said, this particular query
simply isn't eligible to use a skip scan. It's impossible for any
single column index to do so.

The best guess I have is that the skip scan commit inadvertently added
planner cycles, even though this query isn't eligible to use skip scan
-- I thought that I'd avoided that, but perhaps I overlooked some
subtlety.

Can you try it again, with prepared statements? Alternatively, you
could selectively revert the changes that commit 92fe23d93aa made to
utils/adt/selfuncs.c, and then retest.

-- 
Peter Geoghegan