Horton

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

Tomas Vondra <tomas@vondra.me>

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From: Tomas Vondra <tomas@vondra.me>
To: Peter Geoghegan <pg@bowt.ie>
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: 2025-05-09T14:51:10Z
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 5/9/25 16:17, Peter Geoghegan wrote:
> On Fri, May 9, 2025 at 8:58 AM Tomas Vondra <tomas@vondra.me> wrote:
>> I'm also not sure about the root cause, but while investigating it one
>> of the experiments I tried was tweaking the glibc malloc by setting
>>
>>     export MALLOC_TOP_PAD_=$((64*1024*1024))
>>
>> which keeps a 64MB "buffer" in glibc, to reduce the amount of malloc
>> syscalls. And with that, the results change to this:
> 
> You're sure that the problem is an increase in the number of
> malloc()s? If that's what this is, then it shouldn't be too hard to
> debug.
> 

No, I'm not sure. I merely speculate based on the observation that
setting the environment variable makes the issue go away.

I've seen similar problems with btree before, as it allocates fairly
large chunks of memory for BTScanOpaque.


-- 
Tomas Vondra