Domains
ALTER DOMAIN ... ADD CONSTRAINT
ALTER DOMAIN order_status_domain ADD CONSTRAINT valid_status CHECK (VALUE IN ('pending','paid'));What this does
Validates the new constraint against every column, on every table, that uses the domain, all at once. SHARE blocks writes (not reads) on each of those tables for the duration, which is a wide, hard-to-predict blast radius compared to adding a CHECK to a single table.