Horton

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: Andrey Borodin <x4mmm@yandex-team.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Andres Freund <andres@anarazel.de>, Robert Haas <robertmhaas@gmail.com>, Heikki Linnakangas <hlinnaka@iki.fi>
Date: 2025-09-02T21:52:37Z
Lists: pgsql-hackers

Commits

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

  1. Remove table_scan_analyze_next_tuple unneeded parameter OldestXmin

  2. Simplify visibility check in heap_page_would_be_all_visible()

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

  4. Combine visibilitymap_set() cases in lazy_scan_prune()

  5. Fix const qualification in prune_freeze_setup()

  6. Simplify vacuum visibility assertion

  7. Split heap_page_prune_and_freeze() into helpers

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

  9. Split PruneFreezeParams initializers to one field per line

  10. Refactor heap_page_prune_and_freeze() parameters into a struct

  11. Make heap_page_is_all_visible independent of LVRelState

  12. Inline TransactionIdFollows/Precedes[OrEquals]()

  13. Add helper for freeze determination to heap_page_prune_and_freeze

  14. Bump XLOG_PAGE_MAGIC after xl_heap_prune change

  15. Correct prune WAL record opcode name in comment

  16. Add error codes when vacuum discovers VM corruption

  17. Remove unused xl_heap_prune member, reason

  18. Remove unneeded VM pin from VM replay

  19. Add assert and log message to visibilitymap_set

  20. Add error codes to some corruption log messages

On Thu, Aug 28, 2025 at 5:12 AM Kirill Reshke <reshkekirill@gmail.com> wrote:
>
> I did micro git-blame research here. I spotted only one related change
> [0]. Looks like before this change pin was indeed needed.
> But not after this change, so this visibilitymap_pin is just an oversight?
> Related thread is [1]. I quickly checked the discussion in this
> thread, and it looks like no one was bothered about these lines or VM
> logging changes (in this exact pin buffer aspect). The discussion was
> of other aspects of this commit.

Wow, thanks so much for doing that research. Looking at it myself, it
does indeed seem like just an oversight. It isn't harmful since it
won't take another pin, but it is confusing, so I think we should at
least remove it in master. I'm not as sure about back branches.

I would like someone to confirm that there is no way we could end up
with a different block of the VM containing the vm bits for a heap
block during recovery than during normal operation.

- Melanie