Database Connection Pooling

1. The Pattern

Opening a database connection is expensive; running a query on one is cheap. So open a small number of connections once, keep them alive, and let requests borrow and return them.

First, understand the cost being avoided. A new database connection is a TCP handshake, a TLS negotiation, and authentication. That is 20-50 ms before your first query. On the database side it is not just time. In Postgres, each connection is a dedicated server process holding real memory. Meanwhile the query you wanted to run takes 5 ms