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1. Two source clusters hash to the same 32-bit region. Collision risk is ~1 in 4 billion per cluster pair.
2. Both clusters have an active producer with the same local PID. This is likely since Kafka allocates them sequentially from 0.

With a small number of source clusters (say 2-5), the probability of collision 1 is negligible. With many sources, the birthday paradox applies: you would need ~65,000 source clusters before reaching a 50% chance that any two share a hash. That is well beyond any realistic deployment.

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