If you want to read about the theoretical underpinnings, Cassandra is derived from the original Dynamo paper[0] from Amazon, and Scylla is a drop-in replacement for Cassandra written in C++ instead of Java. Cockroach follows more closely the Google Spanner[1] approach.
For a more practical summary, compare the architecture overviews of Cassandra[2] and Cockroach[3].
For a more practical summary, compare the architecture overviews of Cassandra[2] and Cockroach[3].
0: http://www.allthingsdistributed.com/files/amazon-dynamo-sosp...
1: https://static.googleusercontent.com/media/research.google.c...
2: https://docs.datastax.com/en/cassandra/3.0/cassandra/archite...
3: https://www.cockroachlabs.com/docs/stable/architecture/overv...