Datastax Cassandra Administrator Certification Questions and Answer (Pratice Questions and Dumps)

Question-: Once you have removed a node from the Cassandra cluster, using the “nodetool decommission� command. Which of the following is correct?
A. Node will go offline
B. JVM process would be running on this node
C. Data would not be deleted from the decommissioned node.
D. If you want to add this node back to the cluster, then you should not delete this data.

Answer: A, B, C

Explanation: When you run “nodetool decommission� command on existing live node. Following this would be taken care and note down.
- Node will go offline, once decommissioning process finishes.
- However, JVM process would still be running on the cluster. And you should use the “cassandra-stop� command to kill this Java process.
- Decommission process would not delete the data from the decommissioned node. You have to explicitly delete the data.
- If you don’t delete the data then there would be data resurrection issues happened, when you add node back to the cluster.



Question-: In Cassandra cluster, once of the node is trying to get the gossip info from the node, it was already doing. But somehow, it is not able to get the gossip info. Then what would happen in this case?
A. The node would not get the gossip info then it will retry after 15 mins to get the info from same node.
B. Node will become offline. As it does not have gossip info.
C. Node will try to gossip info from the next neighboring node.
D. Node will connect to the seed nodes to get the gossip info

Answer: D

Explanation: Whenever node does not get the gossip info required then it would fall back to the seed nodes to get the gossip info. Hence, you should always configure the list of seed node info in the configuration file.



Question-: You are running node Cassandra cluster, and you found that one of the node in the cluster is dead. You want to replace that node with the new node. Which of the following correctly applies in this situation?
A. You have to manually copy the data from the dead node to the new node. Before adding to the cluster. So that replacement is quick.
B. You must have tested this node by adding to this cluster and it may have created directories for the data, save_caches, commitlog and hints.
C. You can not replace the nodes in the single-token cluster architecture.
D. Node you are adding to the cluster must not have previous data in the data directory, saved_caches, commitlog and hints.

Answer: D

Explanation: Yes, the node you are going to add should be cleaned node. You should add the only new node to the cluster. A new node is a system that you have never added to the cluster (if done, then format and clean that node, to make it new). This new node must have absolutely no previous data in the data directory, saved_caches, commitlog and hints. Adding nodes previously used for testing or that have neen removed from another cluster, merges the older data into the cluster and may causes data loss or corruption.

Related Questions

---

Question-: You have node Apache Cassandra cluster where consistency level is set as QUORUM as well as replication factor is . (CL=QUORUM , RF=). When write happens and one of the node goes down, what would happen in this case (other settings are default)?

A. Coordinated node will store the hint
B. As writes already done on 2 nodes, it will return successful write.
C. Coordinated node will return UnavailableException
D. When failed nodes comes back after 6 hours, coordinated nodes will replay the hint. So that 3rd copy of data will be created.


Question-: You have node cluster with setting as CL=ANY and RF=, What happen when all the nodes are down where data needs to be written (Assume other settings are default)?

A. It means coordinator node will store the hints.
B. Even all 3 nodes are down, it will return successful write.
C. It will wait for one of the 3 nodes to come back until than write will hangs.
D. If all the nodes come back after 4 hours all the replicas will be copied from coordinated node.
E. None of the above


Question-: Which of the following would help in keeping the data in sync across the cluster?
A. Hinted Handdoff
B. Read Repair
C. Anti-entropy repair


Question-: You have consistency level set as ONE. Would always have a read repair operation as blocking?
A. True
B. False



Question-: You see that your Cassandra database is occasionally not in Sync and you decided to enable the NodeSync utility. What all are correct for this utility?
A. You have to schedule the NodeSync activity which can periodically e.g. every 4 hours.
B. It has a high impact on the Cluster performance.
C. This does not require manual intervention.
D. Each node should run the NodeSync service.
E. NodeSync is enabled for per table basis and it validates the local data ranges for NodeSync-enabled tables and repairs any inconsistency found.
Ans; C,D,E
Exp: NodeSync is an utility service to repair the data in Cassandra database. This service runs in the background. This has low overhead and provides consistent performance and minimal manual effort required like just enabling it. It has following features
- Continuously validates that data is in sync on all replica.
- Always running but low impact on cluster performance.
- Fully automatic, no manual intervention needed.
- Completely replace anti-entropy repairs.
Each node runs the NodeSync service, and remain idle if there is nothing to validate. It needs to be enabled on per table basis, which continuously validates the local data ranges for the tables on which this is enabled.

Remember: when NodeSync is enabled on the table, then running repair command on that particular table will be rejected.

Admin only

Question-: Which of the following statement is/are correct?
A. Vnode helps in determining partition range and rebalancing the cluster when adding or removing nodes.
B. You must have same token architecture across the entire cluster. Means all the nodes should be vnodes enabled or single-token architecture.
C. You can have one of the Datacenter as transaction only in same cluster.
D. When adding more than once nodes to the cluster using allocation algorithm they should not be added altogether and should be done one by one.


Question-: You have a Cassandra cluster enabled with the vnodes. How can you disable the same?
A. We need to comment the num_tokens in cassandra.yaml file
B. We need to comment the allocate_tokens_for_loal_replication_factor in cassandra.yaml file
C. Uncomment the initial_token and set it to 1.
D. Comment the initial_token
E. Uncomment num_tokens and set it with the 8