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

Kirill Reshke <reshkekirill@gmail.com>

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From: Kirill Reshke <reshkekirill@gmail.com>
To: Melanie Plageman <melanieplageman@gmail.com>
Cc: Alexander Lakhin <exclusion@gmail.com>, Andres Freund <andres@anarazel.de>, Andrey Borodin <x4mmm@yandex-team.ru>, Chao Li <li.evan.chao@gmail.com>, Xuneng Zhou <xunengzhou@gmail.com>, Robert Haas <robertmhaas@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Heikki Linnakangas <hlinnaka@iki.fi>
Date: 2026-01-30T09:23:07Z
Lists: pgsql-hackers 
On Thu, 29 Jan 2026 at 20:16, Melanie Plageman
<melanieplageman@gmail.com> wrote:
>
> On Thu, Jan 29, 2026 at 8:39 AM Kirill Reshke <reshkekirill@gmail.com> wrote:
> >
> > Thanks Alexander!
> > This is a good and detailed report, I was able to reproduce this.
>
> Thanks to both of you for looking into it!
>
> > I have added some logs to my copy of postgres with your patch and I
> > think problem causing this test to fail is this sequence:
> >
> > 1) Autovacuum starts, does its deeds, and acquiring xid = 118518
>
> So, in this scenario, is the issue that autovacuum runs before vacuum
> freeze? If so, we can change the table DDL to:
>
> create table test_vac_unmodified_heap(a int) with (autovacuum_enabled = false);
>
> which would prevent the autovacuum from running.

Hi!
Yes I did try this, but it does not help, because autovacuum runs on
catalog relations, still causing fail.


> Unless there is some other way for one of the other tests to hold
> OldestXmin back to before the xid of the insert. But I don't see how.
>
> > 2) insert into test_vac_unmodified_heap values (1); executes and
> > commits with xid = 118519 (from my log)
> > 3) vacuum freeze starts and computes cutoff xid = 118518, because
> > oldest xmin is 118518 from (1)
> >
> > *and we cannot freeze tuple*
>
> - Melanie



-- 
Best regards,
Kirill Reshke

On Thu, 29 Jan 2026 at 20:16, Melanie Plageman
<melanieplageman@gmail.com> wrote:
>
> On Thu, Jan 29, 2026 at 8:39 AM Kirill Reshke <reshkekirill@gmail.com> wrote:
> >
> > Thanks Alexander!
> > This is a good and detailed report, I was able to reproduce this.
>
> Thanks to both of you for looking into it!
>
> > I have added some logs to my copy of postgres with your patch and I
> > think problem causing this test to fail is this sequence:
> >
> > 1) Autovacuum starts, does its deeds, and acquiring xid = 118518
>
> So, in this scenario, is the issue that autovacuum runs before vacuum
> freeze? If so, we can change the table DDL to:
>
> create table test_vac_unmodified_heap(a int) with (autovacuum_enabled = false);
>
> which would prevent the autovacuum from running.
>
> Unless there is some other way for one of the other tests to hold
> OldestXmin back to before the xid of the insert. But I don't see how.
>
> > 2) insert into test_vac_unmodified_heap values (1); executes and
> > commits with xid = 118519 (from my log)
> > 3) vacuum freeze starts and computes cutoff xid = 118518, because
> > oldest xmin is 118518 from (1)
> >
> > *and we cannot freeze tuple*
>
> - Melanie



-- 
Best regards,
Kirill Reshke

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