I have a Cassandra story as well. At a previous employer our org used a database that was a custom wrapper around Cassandra. This was a fairly large organization and this particular database was the keystone to the vast majority of operations of this particular organization. Well, one day I was giving a demo to some junior devs on how to use the REST API for the database which just so happened to take in raw Solr queries. I always liked to point that out to the newer devs as a way they could do some nice things that were otherwise fairly limited by the REST API.

Well, one of the junior devs just so happened to be playing around with various different Solr queries to see what he could get back and somehow issued a query that caused the entire staging database to fall over. That was a fun phone call to get. It wasn’t the junior dev’s fault, of course, but it really did wonders to expose the fragility of poorly optimized/unindexed queries against the database.

My experience in general with Cassandra is that outside of a few experts working with it, it was pretty poorly understood throughout the org and no one except those select people could really do anything when it all fell over.