Using Postgres at scale often necessitates the use of a connection pooler like PgBouncer to manage concurrent queries efficiently without overwhelming the database. PgBouncer, which has been in use since 2014, allows applications to handle large bursts of queries by queuing them in the connection pooler instead of directly on the database, thus optimizing performance and reducing memory usage per connection. It is wire-compatible with database clients, allowing for seamless integration without code changes. Despite its utility, understanding and troubleshooting PgBouncer can be challenging due to the cryptic nature of some of its diagnostic outputs, such as SHOW POOLS, which displays connection pool statuses. The article delves into defining various states of client and server connections, explaining how they interact within PgBouncer, and discusses potential issues like high waiting times or misconfigurations that might lead to inefficiencies. The text also provides insights into configurable limits and failure scenarios within PgBouncer, alongside a brief overview of relevant code files for those interested in exploring its internal workings.