pgsql: Clamp result of MultiXactMemberFreezeThreshold

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

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a5662ba345e732c1f714409b38b75be98105aab6

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