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

4.2. PERFORMANCE MODELING PATTERN 69
Pattern 10: Round-robin Load Balancer
Load Balancer
T1: Round Robin
Consumer 1
Event
Consumer 1
Load Balancer
Event
Consumer 2
Event
...
...
...
Load
Balancer
T1
...
Consumer 2
Consumer n
NextIsC1
NextIsC2
...
NextIsCn
Consumer n
Event
Load Balancer
NextIsC1
...
NextIsC2
Figure 4.19: Load Balancer - Round Robin
Characteristics
• Load balancing
• Round-robin
Example
Incoming events are processed by a load balancer and afterwards distributed among event consumers
in a round robin manner. Each event is forwarded to exactly one consumer.
Description
Incoming events are arriving at the place Load Balancer and forwarded to the Consumer by
transition T1. For each Consumer exists an own mode in transition T1. Further, a token named
NextIsC i is defined. i is the unique id of the consumer, e.g. for Consumer 1 the color name is
NextIsC1. To implement a round robin behavior the load balancer needs to keep track which
Consumer is next. We model this knowledge by storing a NextIsC i token in the Load Balancer.
This token identifies the Consumer i who should receive the next Event. As illustrated in Figure
4.19, the modes of transition T1 takes into account, which consumer is next and update the
state of the Load Balancer by replacing the NextIsC i token with a NextIsC i+1 token.
For example, if an Event token and a NextIsC1 token are stored in the depository place
of the load balancer, the corresponding mode of transition T1 is fired. The Event token is
forwarded to Consumer 1 and the NextIsC1 token is replaced by a NextIsC2 token.
To initialize the model we have to specify the consumer that should receive the first Event
token. This is done by initializing the corresponding NextIsC i token.