Cary Huang digs into one phase of Postgres query processing:
When you send a query to PostgreSQL, it normally would go through stages of query processing and return you the results at the end. These stages are known as:
- Parse
- Analyze
- Rewrite
- Plan
- Execute
I wrote another blog to briefly explain the responsibility of each query processing stage. You can find it here. In this blog, we will only focus on the “plan” stage or the “planner” module as this is perhaps the most interesting or complex stage if you will. I will share my understanding of the planner module as I investigate its internal workings to handle a simple sequential scan. This will be based on PostgreSQL 16.
Read on to learn what the planner does and how it works, at a high level.