Node decommissioning and scaling in Hadoop - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Node Decommissioning Purpose

Why is node decommissioning important in a Hadoop cluster?

A It automatically upgrades the node's hardware without downtime.

B It speeds up data processing by shutting down all nodes simultaneously.

C It allows safe removal of nodes without data loss by redistributing data blocks.

D It permanently deletes all data stored on the node before removal.

💡 Hint

Think about what happens to data when a node is removed.

Decommissioning ensures data blocks on the node are copied to other nodes to prevent data loss before the node is removed.

❓ Predict Output

intermediate

Output of Node Decommissioning Status Command

What is the output of the following command snippet when checking node decommissioning status?

Hadoop

hdfs dfsadmin -report | grep Decommissioning

A Decommissioning nodes: 0

B No decommissioning nodes found

C Error: Command not found

D

Decommissioning nodes: 2
Node1
Node2

💡 Hint

Consider what the command does and what it filters.

The command lists nodes currently being decommissioned, so it shows the count and their names.

❓ data_output

advanced

Data Block Distribution After Node Decommissioning

Given a Hadoop cluster with 5 nodes and replication factor 3, if one node is decommissioned, how many copies of each data block remain after decommissioning completes?

A 3 copies, redistributed to remaining 4 nodes

B 2 copies, because one node is removed

C 1 copy, on a single node only

D 4 copies, due to automatic replication increase

💡 Hint

Think about how replication factor affects data safety during node removal.

The replication factor remains the same; data blocks are copied to other nodes to maintain 3 copies.

🔧 Debug

advanced

Identifying Issue in Node Decommissioning Process

Which option shows a likely cause for a node stuck in decommissioning state indefinitely?

A Network issues preventing data replication to other nodes

B Node has no data blocks to replicate

C Decommissioning completed successfully

D Node is offline and removed from cluster

💡 Hint

Consider what could block data movement during decommissioning.

If the node cannot replicate data due to network problems, it will remain stuck in decommissioning.

🚀 Application

expert

Scaling Cluster by Adding Nodes

You want to scale your Hadoop cluster by adding 3 new nodes. Which step should you perform first to integrate them properly?

A Immediately start running MapReduce jobs on new nodes without configuration

B Add new nodes to the cluster configuration and start DataNode services on them

C Decommission existing nodes before adding new ones

D Remove old nodes from the cluster configuration

💡 Hint

Think about how new nodes join a Hadoop cluster.

New nodes must be added to the cluster config and have DataNode services started to join the cluster properly.