What is a bitmap index scan in PostgreSQL and when does the optimizer prefer it?

Question

Advanced SQL Developer — Medium

What is a bitmap index scan in PostgreSQL and when does the optimizer prefer it?

Accepted Answer

A bitmap index scan in PostgreSQL involves building a bitmap of heap page locations from the index, sorting them, and then reading the heap in physical order. The optimizer prefers this method when a query matches a moderate percentage of rows, making it more efficient than a full table scan or sequential scan.