autovacuum_freeze_max_age

PostgreSQL must 'freeze' old rows before the 32-bit transaction-ID counter wraps around. This sets the maximum age (in transactions) a table may reach before autovacuum forces an aggressive freeze vacuum — even if autovacuum is otherwise off.

The default (200 million) is safe for most. On very high-transaction-rate systems, freeze vacuums can pile up; some operators raise it (carefully, up to a couple of billion) to spread them out — but raising it too far shrinks your wraparound safety margin. Monitor table age via pg_class.relfrozenxid / age().

What is transaction-ID wraparound?

PostgreSQL numbers transactions with a 32-bit counter that eventually wraps. Rows must be 'frozen' before that happens or they'd appear to come from the future and vanish. Anti-wraparound autovacuum does the freezing; autovacuum_freeze_max_age is the deadline that forces it.

• vacuum_freeze_min_age
• vacuum_freeze_table_age
• autovacuum_vacuum_insert_scale_factor