From: Melanie Plageman <melanieplageman@gmail.com>
Date: Thu, 26 Jun 2025 18:25:45 +0000 (-0400)
Subject: Simplify vacuum VM update logging counters
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=060f420a03a8d8186423e7d64302b72e01365c20;p=thirdparty%2Fpostgresql.git

Simplify vacuum VM update logging counters

We can simplify the VM counters added in dc6acfd910b8 to
lazy_vacuum_heap_page() and lazy_scan_new_or_empty().

We won't invoke lazy_vacuum_heap_page() unless there are dead line
pointers, so we know the page can't be all-visible.

In lazy_scan_new_or_empty(), we only update the VM if the page-level
hint PD_ALL_VISIBLE is clear, and the VM bit cannot be set if the page
level bit is clear because a subsequent page update would fail to clear
the visibility map bit.

Simplify the logic for determining which log counters to increment based
on this knowledge. Doing so is worthwhile because the old logic was
confusing and misguided.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Discussion: https://postgr.es/m/flat/CAAKRu_a9w_n2mwY%3DG4LjfWTvRTJtjbfvnYAKi4WjO8QXHHrA0g%40mail.gmail.com
---

diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index 09416450af9..8a42e17aec2 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -1872,8 +1872,6 @@ lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf, BlockNumber blkno,
 		 */
 		if (!PageIsAllVisible(page))
 		{
-			uint8		old_vmbits;
-
 			START_CRIT_SECTION();
 
 			/* mark buffer dirty before writing a WAL record */
@@ -1893,24 +1891,16 @@ lazy_scan_new_or_empty(LVRelState *vacrel, Buffer buf, BlockNumber blkno,
 				log_newpage_buffer(buf, true);
 
 			PageSetAllVisible(page);
-			old_vmbits = visibilitymap_set(vacrel->rel, blkno, buf,
-										   InvalidXLogRecPtr,
-										   vmbuffer, InvalidTransactionId,
-										   VISIBILITYMAP_ALL_VISIBLE |
-										   VISIBILITYMAP_ALL_FROZEN);
+			visibilitymap_set(vacrel->rel, blkno, buf,
+							  InvalidXLogRecPtr,
+							  vmbuffer, InvalidTransactionId,
+							  VISIBILITYMAP_ALL_VISIBLE |
+							  VISIBILITYMAP_ALL_FROZEN);
 			END_CRIT_SECTION();
 
-			/*
-			 * If the page wasn't already set all-visible and/or all-frozen in
-			 * the VM, count it as newly set for logging.
-			 */
-			if ((old_vmbits & VISIBILITYMAP_ALL_VISIBLE) == 0)
-			{
-				vacrel->vm_new_visible_pages++;
-				vacrel->vm_new_visible_frozen_pages++;
-			}
-			else if ((old_vmbits & VISIBILITYMAP_ALL_FROZEN) == 0)
-				vacrel->vm_new_frozen_pages++;
+			/* Count the newly all-frozen pages for logging */
+			vacrel->vm_new_visible_pages++;
+			vacrel->vm_new_visible_frozen_pages++;
 		}
 
 		freespace = PageGetHeapFreeSpace(page);
@@ -2915,7 +2905,6 @@ lazy_vacuum_heap_page(LVRelState *vacrel, BlockNumber blkno, Buffer buffer,
 	if (heap_page_is_all_visible(vacrel, buffer, &visibility_cutoff_xid,
 								 &all_frozen))
 	{
-		uint8		old_vmbits;
 		uint8		flags = VISIBILITYMAP_ALL_VISIBLE;
 
 		if (all_frozen)
@@ -2925,25 +2914,15 @@ lazy_vacuum_heap_page(LVRelState *vacrel, BlockNumber blkno, Buffer buffer,
 		}
 
 		PageSetAllVisible(page);
-		old_vmbits = visibilitymap_set(vacrel->rel, blkno, buffer,
-									   InvalidXLogRecPtr,
-									   vmbuffer, visibility_cutoff_xid,
-									   flags);
+		visibilitymap_set(vacrel->rel, blkno, buffer,
+						  InvalidXLogRecPtr,
+						  vmbuffer, visibility_cutoff_xid,
+						  flags);
 
-		/*
-		 * If the page wasn't already set all-visible and/or all-frozen in the
-		 * VM, count it as newly set for logging.
-		 */
-		if ((old_vmbits & VISIBILITYMAP_ALL_VISIBLE) == 0)
-		{
-			vacrel->vm_new_visible_pages++;
-			if (all_frozen)
-				vacrel->vm_new_visible_frozen_pages++;
-		}
-
-		else if ((old_vmbits & VISIBILITYMAP_ALL_FROZEN) == 0 &&
-				 all_frozen)
-			vacrel->vm_new_frozen_pages++;
+		/* Count the newly set VM page for logging */
+		vacrel->vm_new_visible_pages++;
+		if (all_frozen)
+			vacrel->vm_new_visible_frozen_pages++;
 	}
 
 	/* Revert to the previous phase information for error traceback */