Cassandra and Consistency - A Simplified Explaination
Cassandra is architected for read-write (RW) anywhere, enabling any client to connect to any node in any datacenter (DC). The concept of a primary or single master node does not exist in Cassandra. This allows for drastically increased RW times as master node is not taking all the traffic. The flip side is that there is not a single source of truth (SSOT) as you would see in a RDBMS such as MySQL where you assume the master or primary is always correct. Cassandra has abilities to manage this though. REPLICATION FACTOR (RF): This determines how many copies of data exists. CONSISTENCY LEVEL (CL): This determines how many nodes must acknowledge a read or write before an acknowledgement of a write commit or the data is returned. Examples would be ALL, ONE, QUORUM, etc. Effectively a level of assurance that a write occurred or your read is against the freshest data. Let’s look at two nodes for example. WRITES : If the data is simply being split between the two nodes evenly an