Reviewed by Aditya Kumar · Last reviewed 2026-03-24
Architectural logic: Side inputs = small lookup broadcast to all workers; avoid expensive shuffle. Use case: Enrich events with product catalog or user segments. Main PCollection + side input (AsDict/AsIter) → Map with lookup. Why: No large join; each worker has full lookup....
Architectural logic: Side inputs = small lookup broadcast to all workers; avoid expensive shuffle. Use case: Enrich events with product catalog or user segments. Main PCollection + side input (AsDict/AsIter) → Map with lookup. Why: No large join; each worker has full lookup. Scalability: Side input must fit in memory; large lookups use CoGroupByKey. Cost: Broadcast is cheap; oversized side input causes OOM. Best practice: Keep side inputs small; cache when possible; use CoGroupByKey for large joins.
Red Flag: Using side input for large tables—OOM. Pro-Move: 'We use AsDict for 50K-row product table; events enrich in-stream—join cost dropped 80% vs CoGroupByKey.'
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