Yes, this post is about connection queueing, not just pooling. Because connection pooling  pre-created connections as a pool  is a much-celebrated feature. Almost every discussion on connection pool/pgBouncer starts with the overhead of establishing a new connection to PostgreSQL& and how pre-created connections in the pool can save the world. But there is [&]

https://www.percona.com/blog/2021/02/26/connection-queuing-in-pgbouncer-is-it-a-magical-remedy/