Understanding How Plan Cache Based Execution Statistics implemented in PostgreSQL?

Plan Cache Based Execution Statistics is a feature in PostgreSQL that collects and aggregates execution statistics for SQL statements that are stored in the plan cache. This allows users to monitor and analyze the performance of their SQL queries over time and identify potential performance issues.

Here’s how Plan Cache-Based Execution Statistics is implemented in PostgreSQL:

  1. Execution statistics are collected for SQL statements stored in the plan cache. This includes information such as the total number of times a statement has been executed, the total execution time, and the average execution time.
  2. The collected statistics are stored in the pg_stat_statements system catalog, which can be queried to retrieve execution statistics for specific SQL statements.
  3. PostgreSQL provides a set of built-in functions that can be used to monitor execution statistics. These include pg_stat_statements_reset(), which resets the execution statistics for all SQL statements, and pg_stat_statements, which returns a table of execution statistics for all SQL statements in the plan cache.

Here’s an example of how to use pg_stat_statements to monitor execution statistics in PostgreSQL:

— Enable pg_stat_statements if it’s not already enabled
CREATE EXTENSION IF NOT EXISTS pg_stat_statements;
— Reset the execution statistics
SELECT pg_stat_statements_reset();
— Run some SQL queries
SELECT * FROM users WHERE age > 30;
SELECT * FROM products WHERE price > 100;
— Query the pg_stat_statements view to retrieve execution statistics
SELECT query, total_time, calls, rows FROM pg_stat_statements;

In this example, we first create the pg_stat_statements extension if it’s not already enabled. We then reset the execution statistics using the pg_stat_statements_reset() function. We then run some sample SQL queries and finally retrieve the execution statistics for all SQL statements in the plan cache using the pg_stat_statements view.

The output of the final query will include information about each SQL statement that was executed, including the query itself, the total execution time, the number of times the statement was executed, and the number of rows returned.

To monitor execution statistics over time, you can periodically query the pg_stat_statements view and store the results in a separate table or file for analysis. This can help identify trends and potential performance issues in your SQL queries.

Overall, Plan Cache Based Execution Statistics is a powerful feature in PostgreSQL that can help monitor and analyze SQL query performance over time. By collecting and aggregating execution statistics, users can identify potential performance issues and optimize their queries for better performance.

About Shiv Iyer 456 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.