substreams

Substreams are a concept in stream processing where a single input data stream is partitioned into multiple independent substreams. Each substream is typically formed by routing events according to a key or attribute, such as user ID, region, data type, or device. Once divided, each substream can be processed separately, often in parallel, allowing tailored logic, distinct processing rates, and isolated failure handling for different data segments.

In a typical architecture, a splitter or router directs events from the main stream into the appropriate substreams. Individual processors or operator instances subscribe to specific substreams, performing stateful or stateless processing as needed. A downstream component may merge, aggregate, or forward the results from multiple substreams, or publish them to separate destinations. State management is commonly scoped to each substream, which helps contain faults and simplifies consistency guarantees.

Substreams offer several advantages. They enable scalable parallelism by distributing work across multiple processing units. They provide fault isolation, so errors in one substream do not automatically affect others. They also allow differential processing rules, such as applying different SLAs, retention, or enrichment logic per data category. However, designing substreams introduces trade-offs, including potential event ordering challenges, uneven workload distribution (skew), and increased operational complexity in managing many concurrent streams.

Substreams are used across real-time analytics, monitoring, and data pipelines to improve throughput, responsiveness, and customization of processing. They are implemented in various stream processing systems through partitioning, routing, and per-substream state management.