maxconnections

Maxconnections, often written as max_connections, is a configuration setting that caps the number of client connections a service will handle simultaneously. It is used to prevent resource exhaustion and to maintain predictable performance in systems such as database servers, web servers, and application backends. When the limit is reached, additional connection attempts are either queued or rejected with an error, depending on the software.

In practice, the parameter appears with different names in different software. For example, in MySQL it is max_connections and controls the maximum number of client connections; in PostgreSQL it is max_connections in postgresql.conf; in some server stacks the limit may be managed by a connection pool rather than as a hard cap. Some environments also allow per-user or per-application limits to be configured.

Configuring maxconnections interacts with memory usage and file descriptors. Each active connection consumes memory for buffers, context, and per-connection data structures, and each connection typically consumes a file descriptor. Therefore increasing maxconnections raises memory and FD requirements, and operating system limits (such as ulimit on Linux) may need adjustment. If set too low, legitimate traffic may be blocked or cause timeouts under load; if set too high, available resources may be wasted or exhausted by other processes.

Best practices include monitoring actual concurrent connections, sizing maxconnections to peak usage plus a safety margin, using connection pooling where appropriate, and ensuring OS and application limits are aligned. Regular load testing helps validate the chosen limit under expected patterns of usage.