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

Chao Li <li.evan.chao@gmail.com>

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From: Chao Li <li.evan.chao@gmail.com>
To: Melanie Plageman <melanieplageman@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: 2026-01-07T08:14:38Z
Lists: pgsql-hackers 

> On Jan 7, 2026, at 01:31, Melanie Plageman <melanieplageman@gmail.com> wrote:
> 
> On Tue, Jan 6, 2026 at 4:40 AM Andrey Borodin <x4mmm@yandex-team.ru> wrote:
>> 
>>> <v32-0014-Pass-down-information-on-table-modification-to-s.patch>
>> 
>> I've tried to take an attempt to review some patches of this patchset. It's huge and mostly polished.
> 
> I've added attributed your review on the patches you specifically
> mention here (and from previous emails you sent). Let me know if there
> are other patches you reviewed that you did not mention.
> 
>> In a step "Pass down information on table modification to scan node" you pass SO_HINT_REL_READ_ONLY flag in IndexNext() and BitmapTableScanSetup(), but not in IndexNextWithReorder() and IndexOnlyNext(). Is there a reason why index scans with ordering cannot use on-access VM setting?
> 
> Great point, I simply hadn't tested those cases and didn't think to
> add them. I've added them in attached v33.
> 
> While looking at other callers of index_beginscan(), I was wondering
> if systable_beginscan() and systable_beginscan_ordered() should ever
> pass SO_HINT_REL_READ_ONLY. I guess we would need to pass if the
> operation is read-only above the index_beginscan() -- I'm not sure if
> we always know in the caller of systable_beginscan() whether this
> operation will modify the catalog. That seems like it could be a
> separate project, though, so maybe it is better to say this feature is
> just for regular tables.
> 
> As for the other cases: We don't have the relation range table index
> in check_exclusion_or_unique_constraints(), so I don't think we can do
> it there.
> 
> And I think that the other index scan cases like in replication code
> or get_actual_variable_endpoint() are too small to be worth it, don't
> have the needed info, or don't do on-access pruning (bc of the
> snapshot type they use).
> 
>> Also, comment about visibilitymap_set() says "Callers that log VM changes separately should use visibilitymap_set()" as if visibilitymap_set() is some other function.
> 
> Ah, yes, I forgot to remove that when I removed the old
> visibilitymap_set() and made visibilitymap_set_vmbits() into
> visiblitymap_set(). Done in v33.
> 
> - Melanie
> <v33-0001-Combine-visibilitymap_set-cases-in-lazy_scan_pru.patch><v33-0002-Eliminate-use-of-cached-VM-value-in-lazy_scan_pr.patch><v33-0003-Refactor-lazy_scan_prune-VM-clear-logic-into-hel.patch><v33-0004-Set-the-VM-in-heap_page_prune_and_freeze.patch><v33-0005-Move-VM-assert-into-prune-freeze-code.patch><v33-0006-Eliminate-XLOG_HEAP2_VISIBLE-from-vacuum-phase-I.patch><v33-0007-Eliminate-XLOG_HEAP2_VISIBLE-from-empty-page-vac.patch><v33-0008-Remove-XLOG_HEAP2_VISIBLE-entirely.patch><v33-0009-Simplify-heap_page_would_be_all_visible-visibili.patch><v33-0010-Remove-table_scan_analyze_next_tuple-unneeded-pa.patch><v33-0011-Use-GlobalVisState-in-vacuum-to-determine-page-l.patch><v33-0012-Unset-all_visible-sooner-if-not-freezing.patch><v33-0013-Track-which-relations-are-modified-by-a-query.patch><v33-0014-Pass-down-information-on-table-modification-to-s.patch><v33-0015-Allow-on-access-pruning-to-set-pages-all-visible.patch><v33-0016-Set-pd_prune_xid-on-insert.patch>

I see the same problem in 0009 and 0010:

0009
```
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -3570,6 +3570,7 @@ heap_page_would_be_all_visible(Relation rel, Buffer buf,
 	{
 		ItemId		itemid;
 		HeapTupleData tuple;
+		TransactionId dead_after;
 
 		/*
 		 * Set the offset number so that we can display it along with any
@@ -3609,12 +3610,14 @@ heap_page_would_be_all_visible(Relation rel, Buffer buf,
 
 		/* Visibility checks may do IO or allocate memory */
 		Assert(CritSectionCount == 0);
-		switch (HeapTupleSatisfiesVacuum(&tuple, OldestXmin, buf))
+		switch (HeapTupleSatisfiesVacuumHorizon(&tuple, buf, &dead_after))
 		{
 			case HEAPTUPLE_LIVE:
 				{
 					TransactionId xmin;
 
+					Assert(!TransactionIdIsValid(dead_after));
+
 					/* Check comments in lazy_scan_prune. */
 					if (!HeapTupleHeaderXminCommitted(tuple.t_data))
 					{
@@ -3647,8 +3650,10 @@ heap_page_would_be_all_visible(Relation rel, Buffer buf,
 				}
 				break;
 
-			case HEAPTUPLE_DEAD:
 			case HEAPTUPLE_RECENTLY_DEAD:
+				Assert(TransactionIdIsValid(dead_after));
+				/* FALLTHROUGH */
```

0010:
```
 static bool
-heapam_scan_analyze_next_tuple(TableScanDesc scan, TransactionId OldestXmin,
+heapam_scan_analyze_next_tuple(TableScanDesc scan,
 							   double *liverows, double *deadrows,
 							   TupleTableSlot *slot)
 {
@@ -1047,6 +1047,7 @@ heapam_scan_analyze_next_tuple(TableScanDesc scan, TransactionId OldestXmin,
 		ItemId		itemid;
 		HeapTuple	targtuple = &hslot->base.tupdata;
 		bool		sample_it = false;
+		TransactionId dead_after;
 
 		itemid = PageGetItemId(targpage, hscan->rs_cindex);
 
@@ -1069,16 +1070,20 @@ heapam_scan_analyze_next_tuple(TableScanDesc scan, TransactionId OldestXmin,
 		targtuple->t_data = (HeapTupleHeader) PageGetItem(targpage, itemid);
 		targtuple->t_len = ItemIdGetLength(itemid);
 
-		switch (HeapTupleSatisfiesVacuum(targtuple, OldestXmin,
-										 hscan->rs_cbuf))
+		switch (HeapTupleSatisfiesVacuumHorizon(targtuple,
+												hscan->rs_cbuf,
+												&dead_after))
 		{
 			case HEAPTUPLE_LIVE:
 				sample_it = true;
 				*liverows += 1;
 				break;
 
-			case HEAPTUPLE_DEAD:
 			case HEAPTUPLE_RECENTLY_DEAD:
+				Assert(TransactionIdIsValid(dead_after));
+				/* FALLTHROUGH */
```

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.

I know this comment conflicts to one of my previous comments, sorry about that. As I read this patch once and again, I am getting more understanding to it. 

0014
```
+	/* 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.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/

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