How query execution history can help with re-execution

Andrey Lepikhov

Postgres Professional

Software Developer

15:00 (UTC+3) , russian

Postgres is able to build optimal query plans for most practical cases. However, sometimes, for objective reasons, for complex queries or because of open issues in the planner itself, it can make mistakes and produce a suboptimal plan. Because of this, the execution time of such a request can increase tenfold. If the query is executed frequently, then from time to time this query takes longer than it could, and the DBMS as a whole produces a lower TPS. If the planner is able to record his mistakes and take them into account in the subsequent planning of the same query, then this will improve the characteristics of the DBMS during its operation. We present the results of the development of a PostgreSQL DBMS extension that stores the query execution history and implements the planner recommendation mechanism. We show how knowledge about previously executed queries can improve the performance of subsequent ones.