Big Data Analytics MCQs

Block reports help the NameNode maintain accurate block-location metadata.
They complement frequent lightweight heartbeats.

At startup, the NameNode waits for enough block reports and replicas.
It exits safe mode when the file system is considered sufficiently available.

InputFormat creates InputSplits and RecordReaders.
It adapts different file structures to the key-value processing model.

Map input remains in HDFS and can be read again.
The scheduler chooses an available location for the retry.

Identity mapping preserves the input key and value.
It can be useful when only shuffle, sort, or reduce logic is needed.

Warehouses organize curated data for consistent business analysis.
They commonly use schema-on-write and dimensional models.

Failures can affect an entire rack or switch.
Cross-rack replication improves resilience while balancing network cost.

Decommissioning preserves the target replication factor before the node leaves.
It is safer than abruptly shutting down a storage node.

The RecordReader interprets the bytes within a split.
For text input, it commonly emits byte offsets and lines.

The new reducer attempt retrieves the same intermediate partitions again.
Lost mapper output may require only the affected mappers to be rerun.

Identity reduction can preserve framework grouping and sorting results.
It may also serve as a simple pass-through stage.

Consistency means all clients observe a single current value.
Under network partitions, systems may trade this against availability.