PostgreSQL

Pgpool restarts due to "Sorry, too many clients already"

In order to guarantee that the application connection requests are never rejected, and that the connection requests wait until a database connection is available, the following condition should be met:

max_pool * num_init_children <= (max_connections - superuser_reserved_connections)

You can check max_connections and superuser_reserved_connections in PostgreSQL with these queries:

SHOW max_connections;
SHOW superuser_reserved_connections;

Check Relationship between max pool, num init children, and max connections

Keep Pgpool connections at stable level

Without below numbers, idle connections were slowly increasing and had been reaching the limit of max_connections=400 (memory usage was also quickly increasing):

connection_life_time=60
child_life_time=60