Data Milky Way: Distributed Data Systems (NoSQL & CAP)

We talked a little about NoSQL earlier. Let's just skim the surface and talk about some important concepts driving it.

NoSQL Technologies

Note: "Introduction to NoSQL" by Martin Fowler (watch until 10:35, the remaining 45 minutes are out of scope for the course).

CAP Theorem

Watch: "CAP Theorem Illustrated" by Mark Richards

Summary: Pick Two:

• C (consistency)
• A (availability)
• P (partition tolerance)

But is it really true in the real world?

• What unrealistic assumption are we making here?
  • Can we really assume that network communications won’t fail?
  • Is there really such thing as a distributed system that won’t have partitions?
• In Reality: not a binary choice between C and A
• Several NoSQL solutions offer a tunable tradeoff between C and A

Further Reading (bonus content): What is the CAP Theorem? 3 types of NoSQL databases

Summary

A CP system will say “Sorry, I can’t be sure yet” to the client, in order to avoid giving an out-of-date answer.

An AP system tries to spits out an answer even if it might not be the most up-to-date one.

From Wikipedia