Question-: Select correct statement which applies to replication factor for Cassandra. A. Replication factor 1 means each column will be separately copied on every node in cluster from a Row. B. A replication factor 2 means two copies of each row, where each copy is on different node. C. First replica is always considered primary replica, if node crashes which holds primary replica then second replica become primary. D. You should not set replication factor more than number of nodes in the cluster.
Answer: B, D Exp: Replication factor decide how many copies should be kept for each row in a Cassandra cluster. In your Cassandra cluster if you have only one node then there is no point of having replication factor more than 1. Similarly, if there are two nodes then you can have replication factor as 2. Hence, you should not set Replication factor more than number of nodes in cluster. Hence, option-4 is correct. In the Cassandra each row has equal priority there is no concept of primary and secondary replica. Hence, option-3 is not correct. Replication factor always talk about the entire row and not for individual column. Hence, option-1 is out. And option-2 is correct.
(Admin only)
Question-: You are setting up node cluster and you are expecting that in future you may want to expand this cluster to another data center as well, then which of the following statement is correct? A. You will be using NetworkTopologyStrategy B. You should avoid defining number of replicas during keyspace creation. C. You should define the replica placement strategy while creating keyspace. D. You should define which node will act as a master while crating keyspace.
Answer: A,C Exp: Using the replication strategy you can define on which node individual replica should be placed in the cluster. There is no concept of master/slave in Cassandra database. Hence, option-4 is out. Any of the replica is not unique or special in any sense. Every replica of a row is same. As question is asking in future you may want to expand your cluster across other datacenter as well then in this case you have to choose NetworkTopologyStrategy, which is suitable for expanding cluster across datacenter in future. Hence, option-1 is correct. You have to define replica placement strategy and replication factor while creating keyspace. So option-3 is also correct.
Admin Only
Question-: Which of the following statements are correct for the snitch? A. It helps in mapping IP addresses of nodes to physical and virtual locations like racks and datacenters. B. Snitches inform the database about the network topology used. C. GossipingPropertyFileSnitch is recommended in most of the cases. D. A,B E. A,B,C
Answer: E Exp: A snitch helps in mapping IP addresses of nodes to physical and virtual locations. For example, racks and datacenters. Snitches inform the database about the network topology so that requests are routed efficiently and allows the database to distribute replicas by grouping machines into datacenters and racks. It is mandatory to configure the snitch while creating a cluster. All type of snitches uses a dynamic snitch layer, which monitors performance and chooses the best replica for reading. The dynamic snitch is enabled by default and recommended for use in most deployments. Configure dynamic snitch threshold for each node in the cassandra.yaml configuration file. We should use GossipingPropertyFileSnitch, it helps in defining datacenter and rack. It also uses the gossip protocol for propagating information to other nodes in cluster. Admin Only