Interpreting Plan Nodes
Learn to decipher common plan nodes like sequential scans, index scans, join types, and sorts.
Decoding Query Plans
Welcome back! In the previous lesson, you learned how to use EXPLAIN to view a query's execution plan. Now, let's dive into interpreting the different 'nodes' within these plans.
Each node represents a specific operation PostgreSQL performs. Understanding them is key to identifying performance bottlenecks.
What are Plan Nodes?
Think of a query plan as a tree, where each branch and leaf is a 'node'. These nodes tell you:
- What operation is being done (e.g., scanning, sorting, joining).
- How it's being done (e.g., sequentially, using an index).
- Cost estimates: How much time and resources PostgreSQL *expects* the operation to take.
We'll look at the most common and important node types.