Apache Kafka Kafka Architecture & Internals

Question 1

What is a Kafka 'offset'?

Accepted Answer

A sequential integer that uniquely identifies each message's position within a partition

Answer

The number of bytes from the start of a log file

Answer

A consumer group's processing delay metric

Answer

A broker-assigned message UUID

Question 2

What does 'exactly-once semantics' (EOS) in Kafka require?

Accepted Answer

Idempotent producers plus Kafka transactions to ensure each message is processed and committed once

Answer

Only acks=1 on the producer

Answer

Setting max.in.flight.requests.per.connection=1

Answer

Enabling log compaction on the topic

Question 3

What is a Kafka 'transaction'?

Accepted Answer

An atomic operation that writes to multiple topics/partitions and commits consumer offsets as a single all-or-nothing unit

Answer

A scheduled batch job in Kafka

Answer

A distributed transaction spanning external databases

Answer

A ZooKeeper lock acquired during produce

Question 4

What is the role of the Kafka broker's 'log cleaner' thread?

Accepted Answer

Performs log compaction by removing older duplicate-key records from compacted topics

Answer

Deletes expired messages based on retention.ms

Answer

Compresses log segment files

Answer

Truncates follower logs during leader election

Question 5

What is 'zero-copy' in the context of Kafka's I/O performance?

Accepted Answer

Data is transferred from disk to network buffer directly in the OS kernel without copying through user space

Answer

Messages are stored without serialization overhead

Answer

No replicas means no copy overhead

Answer

The producer reuses message objects without copying

Question 6

What is the 'page cache' and why is it important for Kafka performance?

Accepted Answer

The OS-level disk cache that Kafka relies on to serve repeated reads without physical disk I/O

Answer

An in-memory buffer inside each broker JVM for recent messages

Answer

A Kafka-specific caching layer in front of ZooKeeper

Answer

A client-side cache for recently consumed offsets