TOAST

PostgreSQL TOAST Moves Large Values Outside Heap Rows

PostgreSQL TOAST Moves Large Values Outside Heap Rows PostgreSQL heap tuples cannot span data pages. A row containing a large text, bytea, jsonb, or other variable-length value therefore cannot simply continue onto the next heap page. TOAST provides the storage mechanism that keeps such rows representable: eligible values can be compressed, moved out of line, or both. The visible SQL value does not change when this happens. The physical representation does. A heap tuple may contain a compact reference while the value’s bytes reside as chunk rows in a separate relation associated with the table.