Java Enterprise Best Practices

Distinguish Between Network Lag Time and Server Load

When servers are busy, requests take a longer time to handle. Most of the time, the client simply waits longer. But sometimes, when servers are very busy, a request will simply time out, and an instance of RemoteException will be thrown. In this latter case, retry logic turns out to be fairly painful: if the server is too busy and cannot handle additional requests, the last thing in the world the client should do is send the request again, especially if the request isn’t very important, or can wait awhile.

One way to deal with this is to use what I call the bouncer pattern. The idea is to define a new subclass of Exception, called ServerIsBusy, add it to all the remote methods, and then throw instances of ServerIsBusy whenever the server is too busy to handle additional requests.

In the simplest implementation, the server simply keeps track of the number of pending requests and throws an instance of ServerIsBusy whenever there are too many pending requests, as in the following implementation of the Bouncer class:

public class Bouncer { private static final int MAX_NUMBER_OF_REQUESTS = 73; private static in CURRENT_NUMBER_OF_REQUESTS; private static ServerIsBusy REUSABLE_EXCEPTION = new ServerIsBusy( ); public synchronized static void checkNumberOfRequestsLimit throws ServerIsBusy { if (MAX_NUMBER_OF_REQUESTS == CURRENT_NUMBER_OF_REQUESTS ) { throw REUSABLE_EXCEPTION; } CURRENT_NUMBER_OF_REQUESTS++; } public synchronized static ...