In-sync replicas (ISR) in Kafka - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an In-sync Replica (ISR) in Kafka?

An In-sync Replica (ISR) is a Kafka broker that has fully caught up with the leader's data for a partition. It means the replica has all the latest messages and is ready to take over if the leader fails.

beginner

Why is ISR important in Kafka?

ISR ensures data durability and availability. Only replicas in the ISR can be elected as leaders, which guarantees that no data is lost during failover because these replicas have the latest data.

intermediate

How does a replica join or leave the ISR?

A replica joins the ISR when it catches up with the leader's data within a configured time. It leaves the ISR if it falls behind or becomes unresponsive for too long.

intermediate

What happens if all replicas leave the ISR except the leader?

If all replicas leave the ISR except the leader, Kafka cannot guarantee data durability. The leader continues serving data but the risk of data loss increases if it fails before replicas catch up.

advanced

How does Kafka use ISR to maintain consistency?

Kafka only commits messages when all replicas in the ISR have acknowledged them. This ensures that committed data is safely stored on all in-sync replicas, maintaining consistency.

What does ISR stand for in Kafka?

A Internal Sync Resource

B Instant Sync Replication

C In-sync Replicas

D Independent Sync Replica

ISR stands for In-sync Replicas, which are replicas fully caught up with the leader.

When does a replica leave the ISR?

A When it falls behind or is unresponsive

B When it receives new data

C When it becomes the leader

D When it catches up with the leader

A replica leaves the ISR if it falls behind the leader or becomes unresponsive for too long.

Why does Kafka commit messages only after ISR replicas acknowledge them?

A To ensure data durability and consistency

B To reduce network traffic

C To improve performance

D To allow replicas to lag

Committing messages after ISR replicas acknowledge ensures data is safely stored and consistent.

What risk increases if only the leader remains in the ISR?

A Faster data replication

B Data loss if leader fails

C More replicas joining ISR

D Automatic leader election

If only the leader is in ISR, data loss risk increases if the leader fails before replicas catch up.

Which Kafka component decides the ISR membership?

A Kafka Producer

B Kafka Controller

C Kafka Consumer

D Kafka Broker Leader

The Kafka Broker Leader (partition leader) manages ISR membership by tracking replica states.

Explain what In-sync Replicas (ISR) are and why they matter in Kafka.

Think about how Kafka keeps data safe and available.

Describe the process of how a replica joins or leaves the ISR in Kafka.

Consider what makes a replica 'in-sync' or not.