From b91b3f045abeaad4599bdac9ad7d7f55d7ff234c Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Thu, 13 Jun 2024 19:01:30 +0300 Subject: [PATCH] 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 383c991ced..a676966b87 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