CAP Theorem

Software engineers are likely familiar with the CAP theorem, something coined by Eric Brewer. In short: the CAP theorem posits that distributed databases can have at most 2 of 3 attributes where a database is either consistent, available, or fault tolerant.

In other words, you can have a DB that is consistent and highly available, but not fault tolerant. Or, you can have a DB that’s fault tolerant and highly available, but isn’t always consistent (especially in the event of failure).