Databases & System Design•Part 2: Relational Databases (RDBMS / PostgreSQL / MySQL) (6 - 25)
Database Connection Pooling (PgBouncer):
In Simple Words: Opening database TCP connections is expensive. Connection poolers keep a warm pool of reusable connections, allowing 5,000 app clients to safely share 50 database connections.
sql
-- Monitor active vs idle connections in PostgreSQL:
SELECT state, count(*)
FROM pg_stat_activity
GROUP BY state;