Troubleshooting row lock contention in Amazon Aurora PostgreSQL: Part 1 – Understanding row lock contention in PostgreSQL

This article explains row lock contention in Amazon Aurora PostgreSQL and how to identify it using monitoring tools.

• Row lock contention occurs when multiple transactions compete to update the same rows, causing throughput to drop significantly
• PostgreSQL stores lock information directly in row metadata (xmax) rather than shared memory, enabling efficient concurrent row lock management
• Flash-sale scenarios with 512 concurrent sessions on 25 popular inventory rows reduced throughput by 55% compared to normal distributed load
• Monitor locks using pg_stat_activity, pg_locks views, pgrowlocks extension, and log_lock_waits parameter to detect blocking sessions
• Lock contention appears as Lock:TransactionId, LWLock:LockManager, and Lock:Tuple wait events dominating database load
• Traditional monitoring approaches have limitations: logs are reactive, manual queries require constant monitoring, and pgrowlocks impacts production performance

Understanding PostgreSQL's locking internals and monitoring techniques enables identification of row lock contention patterns in production workloads.