A lightweight PostgreSQL connection pooler that sits between application servers and a PostgreSQL database, multiplexing thousands of application connections onto a small pool of actual database connections. PgBouncer supports session, transaction, and statement pooling modes, with transaction mode providing the best balance of compatibility and efficiency for most web applications.
A SaaS application with 500 concurrent users opens a new PostgreSQL connection per request, overwhelming the database's max_connections=100 limit. Adding PgBouncer in transaction mode allows all 500 application connections to share 20 actual database connections — reducing connection overhead by 96% with no application code changes.