Apache Cassandra
Also written as Cassandra, ScyllaDB, DataStax, Wide-Column Database
A NoSQL database built to spread huge amounts of data across many servers and keep accepting writes even when some servers, or a whole data centre, fail. Used for messaging, activity feeds, IoT and other workloads with enormous write volumes. Data has to be designed around the exact questions the application will ask, which is very different from a traditional database. ScyllaDB is a faster compatible alternative.
Think of it like
A filing system split across many branch offices, each holding copies, so the business keeps running when one branch floods.
Junior or senior?
Hard to run well, so real production experience is differentiating.
Senior sounds like
Talks about designing tables around queries, choosing consistency levels, and keeping the cluster healthy with repairs and compaction.
Ask them
“How did you design your tables around the queries you needed, and what happened when you got that wrong?”