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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: Andres Freund <andres@anarazel.de>
Cc: 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: 2026-03-24T23:44:24Z
Lists: pgsql-hackers

Attachments

Attached v45 is what remains in the patchset (I committed the rest).

On Tue, Mar 24, 2026 at 1:53 PM Andres Freund <andres@anarazel.de> wrote:
>
> On 2026-03-23 17:54:13 -0400, Melanie Plageman wrote:
> > I've made some significant changes to 0006 and realized I need some
> > help. 0006 tracks what relations are modified by a query. This new
> > version (v44) uses relation oids instead of rt indexes to handle cases
> > where the same relation appears more than once in the range table
> > (e.g. INSERT INTO foo SELECT * FROM foo; foo appears twice). It
> > computes modifiedRelOids (a list of relation OIDs modified by the
> > query) in the planner and stores them in the PlannedStmt. There is one
> > big issue I'm not sure how to solve:
>
> I'm not entirely sure this is something we need to catch and therefore not
> sure that modifiedRelOids is worth the trouble over just having the RT
> indexes.

Do you see the disadvantage of saving the oids as the space? I guess
it is also worse (from a semantic perspective) to use oids if the set
is incomplete—for example, because of the insert into leaf partition
case. If they are RT indexes, then it is accurate to say that it
includes all RT indexes for modified rels.

For INSERT INTO foo SELECT * FROM foo, if the pages are mostly full,
setting pages all-visible during the scan won't hurt because we will
insert at the end of the table. And if there is freespace throughout,
we won't do on-access pruning. So, I actually don't think we could end
up setting and unsetting the VM for every page.

In v45, I've gone back to RT indexes.

- 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