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pg_stat_statement – Benefits and Shortcomings [PGSQL Phriday #008]

PGSQL Phriday is a monthly community blog event for the PostgreSQL community, and this month the invitation came from Michael Christofides. Thank you, Michael!

Onwards to the topic … 

As a PostgreSQL DBA, it is essential to have visibility into database performance metrics to optimize database performance. pg_stat_statement is an extension that provides valuable insights into the query performance of a PostgreSQL database.

What is pg_stat_statement?

pg_stat_statement is a PostgreSQL extension that records statistics about the SQL statements executed in a database. It collects query performance data such as the total execution time, the number of times the query was executed, and the total time spent executing the query. pg_stat_statement also records information about the query plan, which can help identify slow queries that require optimization. The statistics collected by pg_stat_statement can be used to monitor database performance, optimize queries, and diagnose performance problems.

How does it collect data?

pg_stat_statement collects data by intercepting SQL statements sent to the database server. Whenever a query is executed, pg_stat_statement records various statistics about the query, such as its execution time, the number of rows returned, and the number of times the query has been executed. This information is stored in a system table called pg_stat_statements.

To enable pg_stat_statement, you need to add it to the list of shared_preload_libraries in your PostgreSQL configuration file (postgresql.conf). Once you have done this, you need to restart the PostgreSQL server to enable the module.

Overhead

pg_stat_statement can cause overhead because it collects detailed performance data about every SQL statement executed in a PostgreSQL database. However, this overhead is minimal and typically has a negligible impact on database performance. The performance overhead of pg_stat_statement can be further reduced by configuring it to only record statistics for specific SQL statements or users.

Shortcomings

pg_stat_statement has a few limitations that PostgreSQL DBAs should be aware of. For example, pg_stat_statement does not record performance data for SQL statements executed within a transaction that was rolled back. Additionally, the information recorded by pg_stat_statement is not persisted across server restarts unless the server is configured to do so explicitly.

Benefits

Despite its shortcomings, pg_stat_statement is an essential tool for PostgreSQL DBAs. It provides a wealth of information about the performance of your database queries. Some of its benefits include:

  1. Identifying slow queries: pg_stat_statement provides detailed performance metrics for each SQL statement executed in a PostgreSQL database. This information can help identify slow queries that require optimization.
  2. Optimizing database performance: By identifying slow queries, PostgreSQL DBAs can optimize database performance and improve query response times.
  3. Improving application performance: Optimizing database performance can improve application performance by reducing the time it takes for queries to execute.
  4. Track change in performance: pg_stat_statement provides a way to track changes in query performance over time, allowing you to monitor the impact of changes to your database schema or query execution plan.

Conclusion

pg_stat_statement is a valuable tool for PostgreSQL DBAs. It provides detailed insights into query performance that can be used to optimize database performance and improve application performance. While it has some limitations, the benefits of using pg_stat_statement outweigh its shortcomings. PostgreSQL DBAs should consider using pg_stat_statement to gain visibility into query performance and optimize database performance.

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