Add the num_conns_sups option

This new option allows configuring the number of connection
supervisors. The old behavior can be obtained by setting this
value to 1. A value larger than num_acceptors will result in
some connection supervisors not being used as the acceptors
currently only use one connection supervisor.

1 files changed, 23 insertions, 3 deletions

diff --git a/doc/src/guide/listeners.asciidoc b/doc/src/guide/listeners.asciidoc
index 4885c6d..e7ecfec 100644
--- a/doc/src/guide/listeners.asciidoc
+++ b/doc/src/guide/listeners.asciidoc
@@ -182,9 +182,9 @@ socket and that it is operational.
 === Limiting the number of concurrent connections
 
 The `max_connections` transport option allows you to limit the number
-of concurrent connections. It defaults to 1024. Its purpose is to
-prevent your system from being overloaded and ensuring all the
-connections are handled optimally.
+of concurrent connections per connection supervisor (see below).
+It defaults to 1024. Its purpose is to prevent your system from being
+overloaded and ensuring all the connections are handled optimally.
 
 .Customizing the maximum number of concurrent connections
 
@@ -261,6 +261,26 @@ measure to find the best value for your application.
 	echo_protocol, []
 ).
 
+=== Customizing the number of connection supervisors
+
+By default Ranch will use one connection supervisor for each
+acceptor process (but not vice versa). Their task is to
+supervise the connection processes started by an acceptor.
+The number of connection supervisors can be tweaked.
+
+Note that the association between the individual acceptors and
+connection supervisors is fixed, meaning that acceptors will
+always use the same connection supervisor to start connection
+processes.
+
+.Specifying a custom number of connection supervisors
+
+[source,erlang]
+{ok, _} = ranch:start_listener(tcp_echo,
+	ranch_tcp, #{socket_opts => [{port, 5555}], num_conns_sups => 42}],
+	echo_protocol, []
+).
+
 === When running out of file descriptors
 
 Operating systems have limits on the number of sockets