Multixact ID wraparound forces emergency autovacuum despite disabled autovacuum

When a table's pg_class.relminmxid age reaches autovacuum_multixact_freeze_max_age (default 400 million multixacts), the system launches autovacuum processes to prevent multixact ID wraparound even when autovacuum is otherwise disabled. This allows removal of old pg_multixact files.

Monitor database_wraparound_age_datminmxid metric to track proximity to multixact wraparound threshold. If approaching limit, manually run VACUUM on affected tables during maintenance windows. Consider reducing autovacuum_multixact_freeze_max_age for individual tables with high multixact usage. Enable autovacuum globally to prevent emergency vacuums.