Update more obsolete multixact.c comments.

petergeoghegan · petergeoghegan · commit 8f8f11593258 · 2023-01-24T15:15:33.000-08:00
Update some remaining comments in multixact.c that still described SLRU truncation as happening in the checkpointer, rather than during VACUUM. Follow-up to commit 5212d44. Shi yu, with tweaks by me. Author: Shi yu <shiy.fnst@fujitsu.com> Discussion: https://postgr.es/m/OSZPR01MB631066BF246F8F74E83222FCFDC69@OSZPR01MB6310.jpnprd01.prod.outlook.com
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
@@ -261,7 +261,7 @@ typedef struct MultiXactStateData
 	 * we compute it (using nextMXact if none are valid).  Each backend is
 	 * required not to attempt to access any SLRU data for MultiXactIds older
 	 * than its own OldestVisibleMXactId[] setting; this is necessary because
-	 * the checkpointer could truncate away such data at any instant.
+	 * the relevant SLRU data can be concurrently truncated away.
 	 *
 	 * The oldest valid value among all of the OldestMemberMXactId[] and
 	 * OldestVisibleMXactId[] entries is considered by vacuum as the earliest
@@ -669,8 +669,8 @@ MultiXactIdSetOldestMember(void)
  *
  * We set the OldestVisibleMXactId for a given transaction the first time
  * it's going to inspect any MultiXactId.  Once we have set this, we are
- * guaranteed that the checkpointer won't truncate off SLRU data for
- * MultiXactIds at or after our OldestVisibleMXactId.
+ * guaranteed that SLRU data for MultiXactIds >= our own OldestVisibleMXactId
+ * won't be truncated away.
  *
  * The value to set is the oldest of nextMXact and all the valid per-backend
  * OldestMemberMXactId[] entries.  Because of the locking we do, we can be

Original file line number	Diff line number	Diff line change
`@@ -261,7 +261,7 @@ typedef struct MultiXactStateData`
`261`	`261`	`* we compute it (using nextMXact if none are valid). Each backend is`
`262`	`262`	`* required not to attempt to access any SLRU data for MultiXactIds older`
`263`	`263`	`* than its own OldestVisibleMXactId[] setting; this is necessary because`
`264`		`- * the checkpointer could truncate away such data at any instant.`
	`264`	`+ * the relevant SLRU data can be concurrently truncated away.`
`265`	`265`	`*`
`266`	`266`	`* The oldest valid value among all of the OldestMemberMXactId[] and`
`267`	`267`	`* OldestVisibleMXactId[] entries is considered by vacuum as the earliest`
`@@ -669,8 +669,8 @@ MultiXactIdSetOldestMember(void)`
`669`	`669`	`*`
`670`	`670`	`* We set the OldestVisibleMXactId for a given transaction the first time`
`671`	`671`	`* it's going to inspect any MultiXactId. Once we have set this, we are`
`672`		`- * guaranteed that the checkpointer won't truncate off SLRU data for`
`673`		`- * MultiXactIds at or after our OldestVisibleMXactId.`
	`672`	`+ * guaranteed that SLRU data for MultiXactIds >= our own OldestVisibleMXactId`
	`673`	`+ * won't be truncated away.`
`674`	`674`	`*`
`675`	`675`	`* The value to set is the oldest of nextMXact and all the valid per-backend`
`676`	`676`	`* OldestMemberMXactId[] entries. Because of the locking we do, we can be`