Horton

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

Peter Geoghegan <pg@bowt.ie>

View thread
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: 2025-05-09T15:55:19Z
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 10:57 AM Tomas Vondra <tomas@vondra.me> wrote:
> I see the regression even with variants that actually match some rows.
> For example if I do this:

> so that the query matches 100 rows, I get the same behavior.

That's really weird, since the index scans will no longer be cheap.
And yet whatever the overhead is still seems to be plainly visible. I
would expect whatever the underlying problem is to be completely
drowned out once the index scan had to do real work.

I wonder if it could be due to the fact that I added a new support
function, support function #6/skip support? That would have increased
the size of things like RelationData.rd_support and
RelationData.rd_supportinfo.

Note that "sizeof(FmgrInfo)" is 48 bytes. Prior to skip scan,
RelationData.rd_supportinfo would have required 48*5=240 bytes. After
skip scan, it would have required 48*6=288 bytes. Maybe 256 bytes is
some kind of critical threshold, someplace?

-- 
Peter Geoghegan