Reading EXPLAIN Like a Query Planner: Bitmap Heap Scans Demystified

You see Bitmap Heap Scan in your EXPLAIN output and wonder if something's wrong. Most developers treat it as a red flag, but it's often the planner's smartest choice when you need hundreds or thousands of rows scattered across many pages. Reading the heap in physical order beats random I/O every time. This video walks through real query plans line by line. You'll learn what Heap Blocks exact vs lossy means, when Rows Removed by Index Recheck signals a tuning opportunity, how work_mem affects bitmap precision, and why buffer hit ratios matter. You'll also see how Postgres uses BitmapOr to combine multiple indexes efficiently. By the end, you'll be able to judge any Bitmap Heap Scan plan in seconds and know exactly when to tune and when to move on. This is for backend engineers, database administrators, and anyone who runs EXPLAIN ANALYZE and wants to understand what they're actually looking at instead of guessing. Chapters: 0:00 Intro 0:33 What Is a Bitmap Heap Scan? 1:53 Decoding the EXPLAIN Output 3:29 Recheck Cond and Lossy Bitmaps 6:18 BitmapOr and Multi-Index Scans 7:43 Judging Your Own Plans in Seconds 9:16 Get a free health report Free weekly PostgreSQL health report → https://mydba.dev?utm_source=youtube&utm_m... #postgresql #database #performance #sql