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Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM on-access)

Alexander Lakhin <exclusion@gmail.com>

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From: Alexander Lakhin <exclusion@gmail.com>
To: Melanie Plageman <melanieplageman@gmail.com>, Andres Freund <andres@anarazel.de>
Cc: Tomas Vondra <tomas@vondra.me>, David Rowley <dgrowleyml@gmail.com>, Kirill Reshke <reshkekirill@gmail.com>, Chao Li <li.evan.chao@gmail.com>, Andrey Borodin <x4mmm@yandex-team.ru>, Xuneng Zhou <xunengzhou@gmail.com>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Heikki Linnakangas <hlinnaka@iki.fi>
Date: 2026-04-03T05:00:00Z
Lists: pgsql-hackers 
Hello Melanie and Andres,

31.03.2026 19:19, Melanie Plageman wrote:
> Thanks for the reply! I have committed the patches in this thread and
> marked the CF entry accordingly.

I've come across an interesting failure produced starting from 378a21618:
when using a build made with CFLAGS="-DRELCACHE_FORCE_RELEASE" and
echo "io_method = sync" >/tmp/temp.config, the test run:
TEMP_CONFIG=/tmp/temp.config TESTS=temp make -s check-tests

fails as below:
--- .../src/test/regress/expected/temp.out   2026-02-13 06:15:55.887368624 +0200
+++ .../src/test/regress/results/temp.out    2026-04-03 07:51:36.735504156 +0300
@@ -493,11 +493,7 @@

  -- Check that read streams deal with lower number of pins available
  SELECT count(*), max(a) max_a, min(a) min_a, max(cnt) max_cnt FROM test_temp;
- count | max_a | min_a | max_cnt
--------+-------+-------+---------
- 10000 | 10000 |     1 |       0
-(1 row)
-
+ERROR:  no empty local buffer available
  ROLLBACK;

Could you look please, if it indicates some regression?

Best regards,
Alexander

Commits

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

  1. Stabilize btree_gist test against on-access VM setting

  2. Stabilize plancache test against on-access VM setting

  3. Make local buffers pin limit more conservative

  4. Update FSM during prune/freeze replay even if freespace is zero

  5. Pass down information on table modification to scan nodes

  6. Thread flags through begin-scan APIs

  7. Remove PlannedStmt->resultRelations in favor of resultRelationRelids

  8. Make it cheap to check if a relation is modified by a query

  9. Keep newest live XID up-to-date even if page not all-visible

  10. Add pruning fast path for all-visible and all-frozen pages

  11. Detect and fix visibility map corruption in more cases

  12. Save vmbuffer in heap-specific scan descriptors for on-access pruning

  13. Avoid BufferGetPage() calls in heap_update()

  14. Initialize missing fields in CreateExecutorState()

  15. Prefix PruneState->all_{visible,frozen} with set_

  16. Add PageGetPruneXid() helper

  17. Move commonly used context into PruneState and simplify helpers

  18. Remove table_scan_analyze_next_tuple unneeded parameter OldestXmin

  19. Simplify visibility check in heap_page_would_be_all_visible()

  20. Rename LVRelState VM-related logging counters

  21. Fix flakiness in the pg_visibility VM-only vacuum test by using a temporary table.

  22. Refactor lazy_scan_prune() VM clear logic into helper

  23. Eliminate use of cached VM value in lazy_scan_prune()

  24. Combine visibilitymap_set() cases in lazy_scan_prune()

  25. Fix const qualification in prune_freeze_setup()

  26. Simplify vacuum visibility assertion

  27. Split heap_page_prune_and_freeze() into helpers

  28. Assert that cutoffs are provided if freezing will be attempted

  29. Split PruneFreezeParams initializers to one field per line

  30. Refactor heap_page_prune_and_freeze() parameters into a struct

  31. Make heap_page_is_all_visible independent of LVRelState

  32. Inline TransactionIdFollows/Precedes[OrEquals]()

  33. Add helper for freeze determination to heap_page_prune_and_freeze

  34. Bump XLOG_PAGE_MAGIC after xl_heap_prune change

  35. Correct prune WAL record opcode name in comment

  36. Add error codes when vacuum discovers VM corruption

  37. Remove unused xl_heap_prune member, reason

  38. Remove unneeded VM pin from VM replay

  39. Add assert and log message to visibilitymap_set

  40. Stamp HEAD as 19devel.

  41. Add error codes to some corruption log messages