In the lambda approach, the stream processor consumes the events and quickly produces an approximate update to the view; the batch processor later consumes the same set of events and produces a corrected version of the derived view. The reasoning behind this design is that batch processing is simpler and thus less prone to bugs, while stream processors are thought to be less reliable and harder to make fault-tolerant (see “Fault Tolerance”). Moreover, the stream process can use fast approximate algorithms while the batch process uses slower exact algorithms.
