Performance Modeling and Benchmarking of Event-Based ... - DVS

Chapter 4
Performance Engineering of
Event-Based Systems
As already discussed in Section 2.1, event-based systems differ from traditional software in
several aspects. Since they are used in business critical environments, there is a need for performance
models [101] which allow the user to predict system behavior or analyze certain performance
aspects and to identify possible bottlenecks.
The fact that event consumer and producer are completely decoupled from each other and
communicate using asynchronous patterns, influences the modeling approach for the performance
aspects of event-based systems. Further, dynamic changes and implementations of EBS
in very large scale and distributed environments make it even harder to find the right model
representation for a given scenario.
As a consequence, we have to investigate whether and how traditional performance modeling
approaches can be applied on EBS. Our first step is to redefine the performance metrics to reflect
particular properties of EBS.
For example, when a request is sent in a traditional request/reply-based distributed system,
it is sent directly to a given destination which makes it easy to identify the system components
and resources involved in its processing. The response time in such an environment can be
defined as time needed by the client to trigger the request and by the server to reply to the
request (see Figure 4.1(a)). The client is blocked while waiting for the answer of the server. This
understanding of response time is not applicable to EBS systems. When an event is published
in an EBS, it is not addressed to a particular destination, but rather routed along all paths
that lead to subscribers with matching subscriptions. Since event producer and consumers are
decoupled, the event producer does not wait for an acknowledgement by the event consumer.
As illustrated in Figure 4.1(b), from the perspective of the event producer the response time
does include the execution time of the event consumer nor the time needed to forward the event
notifications to the n consumers by the transport layer. Therefore, it is questionable whether
metrics such as response time are still appropriate in a decoupled and asynchronous environment
and we see a need for new metrics.
The high concurrency in EBS, their flexibility and the large number of events pose high
requirements to the efficiency and features of modeling technologies. Challenges are, e.g., the
correct representation of event forking, changing or durable subscriptions as well as mobile consumers
and, especially in real world scenarios with thousands or millions of events, a reasonable
solving time for the models is mandatory.
In this chapter, we present our contributions to the area of performance engineering of eventbased
system.
Formal Definition of EBS:
33