Beyond "Pick Two": Real-World Trade Offs

This is Part 4 of a 4-part series on the CAP Theorem and distributed systems trade-offs. Read Part 1, Part 2, or Part 3 if you haven’t already. We’ve dedicated three posts to treating CP and AP as binary choices. etcd is CP. DynamoDB is AP. Pick a side. But that’s not how real systems work. MongoDB can be CP or AP depending on your configuration. Cassandra lets you choose per query. Even PostgreSQL, which we covered as a CP system in Part 2, flips to AP behavior with async replication. The line between strong consistency and high availability isn’t a binary switch…..it’s a spectrum. And then there are the systems that seem to ignore CAP entirely. Google Spanner claims to be both consistent and available. CockroachDB markets itself as “ACID at scale.” What’s going on? The answer comes down to understanding what CAP actually constrains, what happens when networks don’t partition, and how some very smart engineers found ways to work around the edges. FINAL PART OF THE SERIES. SUBSCRIBE TO