Distributed Systems Definitions

Summary

• Definition
• Example
• Happened Before Relationship

Definition

Distributed System is:

• a collection of nodes
• interconnected via LAN/WAN, that can only communicate through sending messages over network
• where the time for communication between nodes is much greater than the time to execute an even on a single node.

A system is “distributed” if the message transmission time, $T_m$ is not negligible to the time between events in a single process, $T_e$.

Leslie Lamport

Example

Events are totally ordered:

• h -> i, f -> g

Send before receive

• a -> b, e -> f

Happened Before Relationship

“a -> b” means either:

• a runs before b on the same process
• a sent a message to b

“a || b” means a and b are concurrent