Analysis and Testing of Ajax-based Single-page Web Applications

Figure 4.7 Sequence of Events in the Experimental Environment.
uses Java’s new IO package (NIO). The NIO package follows the event-driven
design, which allows the processing of each task as a finite state machine
(FSM). As the number of tasks reach a certain limit, the excess tasks are absorbed
in the server’s event queue. The throughput remains constant and the
latency shows a linear increase. The Event-driven design is supposed to perform
significantly better than thread-concurrency model (Welsh et al., 2001;
Welsh and Culler, 2003). Jetty also contains a mechanism called Continuations
(Jetty, 2006). This mechanism allows an HTTP request to be suspended and
restarted after a timeout or after an asynchronous event has occurred. This
way less threads are occupied on the server. Note that no other process was
running in this application server other than TCPDump and UNIX top. Their
load on the server and their effect on the results are negligible, since we only
measure the PID of Jetty. Besides, as mentioned, the test machine has 2x Dual
Core processors, and the server never had 100% load, which can be seen in
Section 4.6.2.
The connectivity between the server and DAS3 nodes is through a 100
Mbps ethernet connection.
4.5.3 Example Scenario
Figure 4.7 shows the sequence of events of an example test scenario from the
perspective of the servers:
1. The Service Provider publishes the stock data to the application server
via an HTTP POST request, in which the creation date, the stock ID, and
the stock message are specified.
2. For push: The application server pushes the data to all the subscribers
of that particular stock. For pull: the application server updates the
90 4.5. Distributed Testing