Conference Schedule - PGConf.EU 2019
What's in a Plan?
Time: 09:30 - 10:20
PostgreSQL's EXPLAIN command is a powerful tool, allowing users to expect and understand query plans in detail. However, the output produced by EXPLAIN is not a direct representation of the plan; it omits some information and displays other information in modified form. In this talk, I'll discuss the differences between the plan as displayed by EXPLAIN and what is actually stored in the server's internal data structures. I'll also discuss why the plan includes the information it does, how that information is computed, and how that information is used at execution time. I hope that this will be helpful in understanding the behavior of the PostgreSQL planner and executor as well as in learning to write patches that modify those systems.