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

Melanie Plageman <melanieplageman@gmail.com>

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From: Melanie Plageman <melanieplageman@gmail.com>
To: Chao Li <li.evan.chao@gmail.com>
Cc: Andrey Borodin <x4mmm@yandex-team.ru>, Kirill Reshke <reshkekirill@gmail.com>, Xuneng Zhou <xunengzhou@gmail.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Heikki Linnakangas <hlinnaka@iki.fi>
Date: 2026-01-27T22:58:33Z
Lists: pgsql-hackers 
On Wed, Jan 7, 2026 at 3:15 AM Chao Li <li.evan.chao@gmail.com> wrote:
>
> I believe the reason why we add Assert(TransactionIdIsValid(dead_after)) under HEAPTUPLE_RECENTLY_DEAD is to ensure that when HeapTupleSatisfiesVacuumHorizon() returns HEAPTUPLE_RECENTLY_DEAD, dead_after must be set. So the goal of the assert is to catch bugs of HeapTupleSatisfiesVacuumHorizon().
>
> From this perspective, I now feel dead_after should be initialized to InvalidTransactionId. Otherwise, say HeapTupleSatisfiesVacuumHorizon() has a bug and miss to set dead_after, then the assert mostly like won’t be fired, because it holds a random value, most likely not be 0.

Actually, thinking about it more, I decided to remove the assertions
on dead_after from those patches entirely. I don't use dead_after and
only pass it in because HeapTupleSatisfiesVacuumHorizon requires it.
In fact, I don't care if the function correctly sets dead_after since
I don't use it.

> +       /* set if the query doesn't modify the rel */
> +       SO_HINT_REL_READ_ONLY = 1 << 10,
> ```
>
> Nit: I think it’s better to replace “rel” to “relation”. For a function comment, if there is a parameter named “rel”, then we can use it to refer to the parameter, without such a context, I guess here a while word is better.

k

I'm currently working on a new version that incorporates Andres'
review feedback and will post soon.

- Melanie

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