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How do you join two streams (or a stream to a table) in a streaming system?

You cannot wait for all the data, and buffering an unbounded stream will OOM. The signal is windowed joins with watermarks for stream-stream, lookup joins for stream-table, and a clear story for late and out-of-order events.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.

You cannot wait for all the data, and buffering an unbounded stream will OOM. The signal is windowed joins with watermarks for stream-stream, lookup joins for stream-table, and a clear story for late and out-of-order events.

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