It depends upon what sort of data you’re looking to store and how you’re wanting to store it. If you can get away with using a key-value database (such as Redis), then that would most likely be your most performant option (not to mention the nice simplicity of the data model makes it pleasurable to work with). Otherwise, I’ve heard that ScyllaDB is suppose to be very performant, particularly for a column-family database (it aims to basically be a high performance version of Cassandra).

I can’t speak for mnesia though, since I have no experience with it.

Our blog post about databases

So if you want search by something more than key (key must be unique :)) the option is column base database like Cassandra or Scylla. Cassandra is fast on write and slow on read. Cassandra is also eventually consistent → not CP database type. And it is not easy to maintain Cassandra :). I don’t know about Scyllia.
In other case you will need to create composite key and store collection of records in this key.

CP (Consistency and Partition Tolerance) ?

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I worked short period for a company who uses ScyllaDB, whatever tools, libraries works for CassandraDB they also works for ScyllaDB, like Xandra library
And ScyllaDB is a monster, very highly performant DB and I found this free GUI tool by Netflix this works for both Cassandra and ScyllaDB
If your use case suits for CassandraDB then I recommend to use ScyllaDB