Can you explain what PgBouncer is and how it is used to optimize connections to PostgreSQL?

PgBouncer is a lightweight connection pooler for PostgreSQL that helps optimize database operations by reducing the overhead of establishing and closing connections.

When an application frequently opens and closes database connections, it creates load and delays. PgBouncer maintains a pool of open connections and reuses them for new requests, significantly speeding up operations.

Main modes of PgBouncer:

• Session pooling — a connection is allocated to a client for the duration of a session.
• Transaction pooling — a connection is allocated only for the duration of a transaction, then returned to the pool.
• Statement pooling — a connection is allocated for executing a single SQL statement.

Using PgBouncer is especially beneficial in high-load systems or with many short queries.

Example configuration in the config file:

[databases]
mydb = host=127.0.0.1 port=5432 dbname=mydb

[pgbouncer]
listen_addr = 127.0.0.1
listen_port = 6432
auth_type = md5
auth_file = userlist.txt
pool_mode = transaction

After starting, the application connects to PgBouncer instead of directly to PostgreSQL, improving performance and stability.