How to influence cost based optimizer in PostgreSQL for performance?

PostgreSQL’s cost-based optimizer (CBO) is responsible for determining the most efficient execution plan for a given query. To influence the CBO and improve performance, you can follow these tips:

  1. Keep statistics up-to-date: PostgreSQL’s CBO relies heavily on statistics about the data in the database to generate efficient execution plans. Ensure that statistics are up-to-date by running ANALYZE on tables and indexes regularly.
  2. Use appropriate indexes: The CBO uses indexes to speed up query execution. Ensure that tables have appropriate indexes to support the most common queries. However, adding too many indexes can also slow down writes, so strike a balance.
  3. Configure work_mem: The work_mem configuration parameter determines the amount of memory used for sorting and other operations during query execution. Set this parameter appropriately based on the size of your data and the complexity of your queries.
  4. Adjust cost settings: PostgreSQL provides several configuration parameters that can be used to adjust the cost model used by the CBO. These include cpu_tuple_cost, cpu_index_tuple_cost, and random_page_cost. Adjust these settings to reflect the actual hardware characteristics of your system.
  5. Use query hints: Sometimes, you may want to override the CBO’s decision and force it to use a particular execution plan. To direct the CBO, use query hints like HASH, MERGE, or NESTED LOOP.
  6. Use partitioning: Partitioning can help the CBO by reducing the amount of data that needs to be scanned during query execution. Use partitioning to divide large tables into smaller, more manageable chunks.

By following these tips, you can influence the CBO in PostgreSQL and improve performance for your workload.

About Shiv Iyer 422 Articles
Open Source Database Systems Engineer with a deep understanding of Optimizer Internals, Performance Engineering, Scalability and Data SRE. Shiv currently is the Founder, Investor, Board Member and CEO of multiple Database Systems Infrastructure Operations companies in the Transaction Processing Computing and ColumnStores ecosystem. He is also a frequent speaker in open source software conferences globally.