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

46 CHAPTER 4. PERFORMANCE ENGINEERING OF EVENT-BASED SYSTEMS
Pattern 2: Standard Pub/Sub - Fixed Number of Subscribers
1‘Event!
" n‘Notification
1‘Event 1‘Event 1‘Notification
T2
Create Notifications
1‘Notification
Producer
T1
Publish Event
Broker
T3
Forward Event
Consumers
Transition 2
In T2, for every incoming event n
notifications are created.
Broker
Event
1
n
Broker
Not.
Figure 4.8: Standard Pub/Sub Pattern - Fixed Number of Subscribers
Characteristics
• 1 : n communication (one event is consumed by n consumers)
Example
A fixed number of event consumers subscribe to a topic.
Description
A producer publishes an event, which is received by a broker. The broker notifies the event
consumers (e.g. subscribers of a topic) by sending a notification event to them.
The idea of this pattern is based on the presumption that the service demand per event on
the broker is composed of two parts, the service demand needed for every incoming event and
the aggregated service demands for the notification of the subscribers:
1‘Conf.No 1‘Conf.No
S EventT otal,Broker = S Event,Broker + n · S Notification,Broker (4.19)
Init T0 Controller T2‘
where
Configure Controlller
Creates the configured no.
n : No. of event notifications. of notifications per Event.
S Event,Broker : Service demand for receiving and processing incoming message.
1‘Event 1‘Event 1‘Notification 1‘Notification
S Notification,Broker : Service demand of broker to create, process and send notifications.
We implement the
Producer
T1 service demand in our patterns by using two
Broker
T3 different token colors, one
for the general service
Consumers
Publish costs Event (event) and one for the notifications Forward (notification) Event created by the
broker. Therefore each incoming event is represented by one token event and n tokens of the
color notification, where n is the number of consumers.
In this version of the pattern, we implemented a straight-forward approach for a 1:n communication.
The number of consumers is directly set in the cardinality of the transition (see Figure
4.8). The downside of this approach is, that the number of consumers is fixed in the transition
and therefore cannot be modified without changing the transition (and therefore the structure
of the model). The reason is that cardinality of transitions in standard QPNs is defined as
constant number. To add more flexibility we propose to allow not only constants but also, e.g.,
distribution functions (see Section 4.3).