Examples of CAP Theorem in Practice

The categories become much easier to remember once you attach them to systems you have heard of. This lesson walks through four, two on each side.

For every one, the question to keep in mind is the same: when the network splits, does this system stop or does it answer?

MongoDB: CP

MongoDB replicates data using one primary and several secondaries. Only the primary accepts writes. The secondaries copy from it.

Now lose the primary, either because it crashed or because a partition cut it off from the rest.

The remaining nodes hold an election and promote a new primary