Systems that get too busy can return the too_many_connections error.

When the number of threads_connected exceeds the max_connections server variable, it's time to make a change. Viewing the threads_connected status variable shows only the current number of connections, but it's more useful to see what the value has peaked at, and this is shown by the max_used_connections status variable.

This error may be a symptom of slow queries and other bottlenecks, but if the system is running smoothly this can be addressed by increasing the value of max_connections.