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Little's Law

Requests in progress equal the arrival rate times how long each one takes.

Taught in Chapter 2: Scaling Out.

More from the same chapter

• Bottleneck: The resource that is full and limits the whole system. Relieve it and the next one appears.
• Load balancer: Sits in front of replicas and picks one for each request.
• Scale out: Adding more copies of a server, called replicas (horizontal scaling).
• Scale up: Moving to a bigger machine (vertical scaling).
• Sticky sessions: Sending every request from a user to the same server, because that server holds their session.
• Utilization: How much of a limit (CPU, threads, connections) is in use. Waiting grows sharply as it nears 100%.