Concurrent Reading and Writing using Mobile Agents

The Case of Facebook

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• 30,000 servers

• The new Facebook data center in Prineville, Oregon. The new servers have been redesigned are networked, for energy efficiency, speed-up and for fault-tolerance.
• The set up mimics client-server kind of operation, with the servers having a high level of parallelism. However, the network of servers may also be viewed as a distributed system.

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Objective of the course

• We will not discuss programming issues here, although you can choose a project and work on it at your own initiative. We will discuss about it soon.

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• With some knowledge in networking, it is not difficult to put
• together a distributed system. It is however, much more difficult
• guarantee that it behaves the way we want it to behave.
• Remember that a system that “sometimes work” is no good. We
• will study what are the critical issues, why a system fails, and how
• We can guarantee our design.

Understanding Models and abstractions

How models help

• algorithms

• models

• Real hardware

• Implementation of models

Message passing vs. shared memory

Modeling Communication

• System topology is a graph G = (V, E), where V = set of nodes (sequential processes) E = set of edges (links or channels, bi/unidirectional).
• Four types of actions by a process:
• - internal action
• - input action
• - communication action
• - output action

Example: A Message Passing Model

• A Reliable FIFO Channel
• Axiom 1. Message m sent ⇔ message m received
• Axiom 2. Message propagation delay is arbitrary but finite.
• Axiom 3. m1 sent before m2 ⇒ m1 received before m2.

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