Creating 100k persistent websockets connections, exchanging small strings (with RemoteEndpoint.Basic) and finally disconnecting all connections the memory grows with ~1GB for each 100k. Basically the test is the following: the clients are connecting and sending a hello message to the server; the server is responding with a welcome string and the clients are disconnecting.

The settings in onOpen() callback are:

session.setMaxBinaryMessageBufferSize(10240);
session.setMaxTextMessageBufferSize(10240);
session.setMaxIdleTimeout(120000);
session.getUserProperties().put("ts", System.currentTimeMillis());