CAP, correctly
On This Lesson 4 topics
This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.
In this lesson
state CAP precisely and avoid its common misuse.
Planned topics
- CAP describes behavior during a network partition: choose consistency (refuse some requests) or availability (answer, possibly stale).
- Partitions are not optional in a distributed system, so "pick any two of three" is misleading.
- When there is no partition, you can have both; CAP says nothing about latency.
- "C" here means linearizability, not the "C" in ACID.
- Labels such as "we are AP" describe one operation or data store under partition, not a whole system.
Draft outline details
Demonstration
a diagram of two replicas with a broken link; a write to replica 1; a read on replica 2 either errors (CP) or returns the old value (AP).
Check your understanding
Does CAP say a CP system is slow when the network is healthy?
Show answer
No; it only describes the choice during a partition.
Practice
Apply this lesson with the module's lab, exercises and quiz.
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