You write with QUORUM, you read with QUORUM. You're safe, right? Although it may seem that way, you could read a different value than the one you wrote - even if nobody else wrote after you. One way this can happen is if the time on the machines in your cluster is not synchronized closely enough. This is called clock skew, and is just one of the ways you'll see that this anomaly can occur. In this talk we'll dive in to how Cassandra handles conflicting data, walk through several weird and seemingly impossible situations that can happen (both with and without clock skew), and see what we can do to work around them. About the Speaker Donny Nadolny Senior Developer, PagerDuty Donny Nadolny is a Scala developer at PagerDuty, working on improving the reliability of their backend systems. He spends a large amount of time investigating problems experienced with distributed systems like Cassandra and ZooKeeper.