Plan operator
Bitmap Index Scan
Plan node that builds a bitmap of matching tuple IDs from one or more indexes before fetching rows from the heap.
A Bitmap Index Scan walks an index and produces a bitmap of every matching row's location, instead of fetching each row immediately. A Bitmap Heap Scan then sorts those locations into page order and reads the heap once per page rather than once per row.
This pattern wins when the planner expects more matches than an Index Scan can chase efficiently, but fewer than would justify a Seq Scan. It also lets PostgreSQL combine multiple indexes via BitmapAnd and BitmapOr — useful when no single index covers the full predicate.
If you see a Bitmap Index Scan dominate a query, check whether a more selective composite index would let the planner switch to a cheaper Index Only Scan instead.