4005-730 Distributed Systems
Lecture Notes -- Module 3. Message Oriented Systems

Message Queuing Systems

• Distributed objects: coupled
  • Both the caller and the callee have to be running at the same time

• Message queuing (MQ) systems: decoupled
  • Messages, not method calls
  • Sender and receiver of a message can be, but need not be, running at the same time
  • Middleware queues messages and guarantees delivery of messages

• MQ APIs
  • Java Message Service (JMS)
  • .NET

• MQ products
  • Amazon Simple Queue Service (SQS)
  • Apache ActiveMQ
  • IBM WebSphere MQ
  • JBoss Messaging → HornetQ
  • Microsoft Message Queuing (MSMQ)
  • OpenJMS

Publish-Subscribe Systems

• Recap: Registry Server remote event capabilities
  • Client can add a listener to receive remote events
  • Client can specify a filter to receive only the events that are of interest
    • Objects bound or unbound
    • Objects of a certain type (implementing a certain interface)
  • P2Pedia System Version 2's monitor

• Publish-subscribe (pub-sub): a generalization
  • A publisher publishes messages
  • A subscriber subscribes to receive messages

• Even more decoupled than MQ systems
  • A publisher need not be aware of who the subscribers are
  • A subscriber need not be aware of who the publishers are

• Message filtering
  • Topic-based
    • Publisher tags each message with the relevant topics
    • Subscriber subscribes to topics and receives all messages tagged with those topics
  • Content-based
    • Subscriber specifies message content or attributes it wants to receive
    • Only matching messages are delivered to subscriber

• Loosely-coupled pub-sub versus tightly-coupled distributed objects
  • Advantages for enterprise and e-commerce applications
  • Examples

• Pub-sub APIs and systems
  • Most message queuing APIs and systems also support pub-sub

• Pub-sub architectures: Message broker (centralized)

• Pub-sub architectures: Decentralized

• A decentralized pub-sub architecture: SIENA
  • A. Carzaniga, D. Rosenblum, and A. Wolf. Design and evaluation of a wide-area event notification service. ACM Transactions on Computer Systems, 19(3):332-383, August 2001.
  • A network of servers, publishers, and subscribers
  • Message content is described by (attribute, value)
  • A publisher broadcasts an advertisement to all servers, stating the kinds of content it will publish
  • A subscriber registers a subscription with its server, stating the kinds of content it wants to receive
  • Servers match advertisements with subscriptions and set up routes based on content
  • A publisher publishes a notification to its server
  • The servers propagate the notification along the appropriate routes
  • The servers send the notification to the interested subscribers
  • Examples

Distributed Systems 4005-730-01 Spring Quarter 2013

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Alan Kaminsky • Department of Computer Science • Rochester Institute of Technology • 4486 + 2220 = 6706

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