What is a sequential scan vs index scan vs parallel scan .... and what is a bitmap heap scan? Postgres scan types explained and diagrammed.

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Explains the different scan types that appear in Postgres EXPLAIN plans and when each is used. Covers sequential scans (reading entire tables row-by-row), index scans (using B-tree indexes to locate data), bitmap index scans (hybrid approach creating in-memory bitmaps), parallel scans (using multiple workers concurrently), and index-only scans (retrieving all data from the index without touching the main table). Includes practical examples showing when each scan type is optimal and how to identify them in query plans.

Postgres Scan Types in EXPLAIN Plans