Enums
ALTER TYPE ... ADD VALUE
PostgreSQL 12+
ALTER TYPE order_status ADD VALUE 'refunded';What this does
The lock is on the type object itself, not on any table that uses the enum, so no table is blocked. Instant on PostgreSQL 12 and later, but the new value cannot be used in the same transaction that added it: using it immediately raises 'unsafe use of new value.'
Safe rewrite
Commit the ADD VALUE before inserting rows that use the new value
-- COMMIT after ADD VALUE, then use the new value in a later transaction.
-- Using it in the same transaction raises: unsafe use of new value "refunded" of enum type order_status