What is checkpointing in distributed stream processing systems?

Checkpointing is the process of periodically saving the state of a stream processing system to enable fault recovery.

In distributed streaming systems, failures are inevitable. Checkpointing ensures that system state (like offsets, aggregations, and in-flight computations) is periodically persisted to durable storage. If a failure occurs, processing resumes from the last checkpoint instead of restarting from scratch. Systems like Spark Structured Streaming and Flink rely heavily on checkpointing to achieve fault tolerance and state consistency.