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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: Kirill Reshke <reshkekirill@gmail.com>
Cc: Chao Li <li.evan.chao@gmail.com>, Xuneng Zhou <xunengzhou@gmail.com>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Andrey Borodin <x4mmm@yandex-team.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Heikki Linnakangas <hlinnaka@iki.fi>
Date: 2026-01-05T19:24:54Z
Lists: pgsql-hackers

Attachments

On Sat, Jan 3, 2026 at 4:36 PM Kirill Reshke <reshkekirill@gmail.com> wrote:
>
> After thinking about it for a week or so, I would actually suggest
> moving forward with v31 (Remove OldestXmin from TAM).
> I think this is a low probability of getting complaints about that.
> Also, we're breaking ABI, so we will know about any important use-case
> not long after 19-beta1.
> Another user of extensible TAM, Cloudberry [0], does not use
> OldestXmin also. I also did not find any user of
> scan_analyze_next_tuple other than postgresql itself with
> http://codesearch.decbian.net/ . Using code-search on github I found
> [1]. Looks like this does not need OldestXmin either.

Thanks for doing this research.

I've attached v32 which is rebased over a change in master and also
resolves the one open issue in the patch set: why the killtuples
isolation test heap accesses count changed after setting pd_prune_xid.

That test creates a table, inserts tuples, accesses one page, deletes
all the data, accesses a single page again (until the table is
vacuumed, the pages will still be there and have to be scanned even
though the data is deleted). The first time we set the VM on-access,
we have to extend the VM. That VM access is an extend and not a hit.
Once we set pd_prune_xid on the page, the extend happens during the
first access (before the delete), so when we access the VM after the
delete step, that is counted as a hit and we end up with more hits in
the stats.

- 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