State stores in Kafka - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a state store in Kafka Streams?

A state store is a local database that Kafka Streams uses to keep track of data and state during stream processing. It helps remember information between events.

beginner

Name two types of state stores in Kafka Streams.

The two main types are:<br>1. KeyValueStore - stores key-value pairs.<br>2. WindowStore - stores data with time windows.

intermediate

How does Kafka Streams keep state stores fault-tolerant?

Kafka Streams backs up state stores by writing changes to a special Kafka topic called a changelog. If the app crashes, it can restore the state from this topic.

intermediate

What is the role of ProcessorContext in accessing state stores?

ProcessorContext provides access to state stores inside a processor. It lets you read and write data to the store during processing.

intermediate

Why use state stores instead of external databases in Kafka Streams?

State stores are local and fast, tightly integrated with Kafka Streams. They reduce latency and simplify managing state compared to external databases.

What does a Kafka Streams state store primarily do?

A Manages user authentication

B Sends messages to Kafka topics

C Stores and manages local state for stream processing

D Creates new Kafka topics

State stores keep local data needed to process streams, like counts or aggregates.

Which Kafka topic type is used to back up state stores for fault tolerance?

A Changelog topic

B Input topic

C Output topic

D Control topic

Changelog topics store all changes to state stores to restore state after failure.

Which interface lets you access state stores inside a Kafka Streams processor?

A StreamBuilder

B KafkaProducer

C KafkaConsumer

D ProcessorContext

ProcessorContext provides methods to access state stores during processing.

What type of state store would you use to keep data grouped by time intervals?

A WindowStore

B KeyValueStore

C SessionStore

D TimestampStore

WindowStore stores data with time windows, useful for time-based aggregations.

Why are state stores preferred over external databases in Kafka Streams?

A They require no configuration

B They are local and faster for stream processing

C They automatically scale Kafka clusters

D They replace Kafka topics

Local state stores reduce latency and simplify state management compared to external databases.

Explain what a state store is and why it is important in Kafka Streams.

Think about how Kafka Streams remembers information between events.

Describe how Kafka Streams ensures state stores are fault-tolerant and can recover after a crash.

Consider how changes to the state are saved and replayed.