In this recipe, we will be discussing various index scans, and how they try to fetch matching tuples from tables.
As we all know, an index is a physical object that can help a query retrieve table data much faster than a sequential scan. In the explain plan, we frequently get index scan, bitmap heap scan, or index only scan node types, which works on a particular index. Whenever an index is scanned, then an immediately followed action would be to return the matching tuples from the index, build a bitmap in memory, or fetch the tuples from the base table.
To demonstrate the index scan, let's run the following simple query and see how many tuples it is reading from the base table:
benchmarksql=# SELECT pg_stat_reset(); ...