Question-146: In Cassandra for write request, how atomicity works?

Answer: In Cassandra a write operation is atomic at the partition level, it means the insertion or updates of two or more rows in the same partition are treated as one write operation. Similarly, delete operation is also atomic at the partition level. 

Question-147: In Cassandra how does isolation works?

Answer: When a delete or a write operation is performed that would be applied at row level, it means that write to a row within a single partition on a single node is only visible to the client performing the operation. The operation is restricted to the scope until it is completed. However, in case of batch all the updates in a batch operation belonging to a given partition key has the same restriction. And in batch operation, this not isolated if it includes changes to more than one partition.

Question-148: Once you configured your cluster, which node you should start first?

Answer: you should consider starting the seed node first.

Question-149: Can you please explain again what are the functions of Snitch?

Answer: Snitch has two function

• It is Snitch responsibility to let Casandra know about network topology to route request efficiently.
• It allows the Cassandra to spread replicas around your cluster to avoid correlated failures. And that can be achieved by grouping machines in to datacenter and racks. Cassandra storage engine will try at its best not to have more than one replica on the same rack. Also remember that it is not necessary that a rack or a datacenter is really a physical location. 

Question-150: How does Cassandra monitor that a node is slowed down?

Answer: Cassandra find the node which has been slowed down in the cluster using the dynamic snitch monitor. There are various properties you have to set to enable and use the dynamic Snitch in Cassandra.yaml file.