Breaking the Microbatch Barrier: The Architecture of Apache Spark Real-Time Mode

Apache Spark 4.1 introduces Real-Time Mode (RTM) for Structured Streaming, enabling millisecond-level latency without abandoning the microbatch architecture.

• •Traditional microbatch processing incurs fixed overhead costs (log writes, state uploads to object storage) that dominate execution time when batch sizes shrink, creating a latency floor.
• •RTM uses longer-duration epochs with continuous data flow, eliminating the per-batch blocking that caused high latency while retaining fault tolerance via checkpointing.
• •Concurrent processing stages allow reducers to start consuming shuffle files as soon as mappers produce them, rather than waiting for full stage completion.
• •Non-blocking operators (e.g., group-by aggregation) minimize buffering and emit results continuously instead of only at batch boundaries.