![[str_idx_hash.png|256]] - **Description**: Stores 32-bit hash codes derived from the column values. Extremely efficient for flat equality checks but useless for ranges or sorting. - **Supported Operators**: `=`. - **Special Features**: - Since PostgreSQL 10, Hash indexes are WAL-logged and crash-safe. - **Metaphor**: A massive wall of identical mailboxes. You don't look through them all; you have a magic key that tells you exactly which one box contains your mail.