Cassandra is not row level consistent
Cassandra developer here.<p>Lots of comments here about how Cassandra is AP so of course you get inconsistent (non-serializable) results.<p>This is true, to a point.  I'm firmly convinced that AP is a better way to build distributed systems for fault tolerance, performance, and simplicity.  But it's incredibly useful to be able to "opt in" to CP for pieces of the application as needed.  That's what Cassandra's lightweight transactions (LWT) are for, and that's what the authors of this piece used.<p>However!  Fundamentally, mixing serializable (LWT) and non-serializable (plain UPDATE) ops will produce unpredictable results and that's what bit them here.<p>Basically the same as if you marked half the accesses to a concurrently-updated Java variable with "synchronized" and left it off of the other half as an "optimization."<p>Don't take shortcuts and you won't get burned.