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commit    b91b3f045abeaad4599bdac9ad7d7f55d7ff234c
Author:   Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date:     Thu Jun 13 16:01:30 2024 +0000
First released in: 17.0, 12.20, 13.16, 14.13, 15.8, 16.4

    Clamp result of MultiXactMemberFreezeThreshold
    
    The purpose of the function is to reduce the effective
    autovacuum_multixact_freeze_max_age if the multixact members SLRU is
    approaching wraparound, to make multixid freezing more aggressive.
    The returned value should therefore never be greater than plain
    autovacuum_multixact_freeze_max_age.
    
    Reviewed-by: Robert Haas
    Discussion: https://www.postgresql.org/message-id/85fb354c-f89f-4d47-b3a2-3cbd461c90a3@iki.fi
    Backpatch-through: 12, all supported versions


 src/backend/access/transam/multixact.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index 383c991ced2..a676966b877 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -2828,6 +2828,7 @@ MultiXactMemberFreezeThreshold(void)
 	uint32		multixacts;
 	uint32		victim_multixacts;
 	double		fraction;
+	int			result;
 
 	/* If we can't determine member space utilization, assume the worst. */
 	if (!ReadMultiXactCounts(&multixacts, &members))
@@ -2849,7 +2850,13 @@ MultiXactMemberFreezeThreshold(void)
 	/* fraction could be > 1.0, but lowest possible freeze age is zero */
 	if (victim_multixacts > multixacts)
 		return 0;
-	return multixacts - victim_multixacts;
+	result = multixacts - victim_multixacts;
+
+	/*
+	 * Clamp to autovacuum_multixact_freeze_max_age, so that we never make
+	 * autovacuum less aggressive than it would otherwise be.
+	 */
+	return Min(result, autovacuum_multixact_freeze_max_age);
 }
 
 typedef struct mxtruncinfo


[parent: 57625308f62d]