When joining sales to a table of tax rates, you probably want to join with the tax rate at the time of the sale, which may be different from the current tax rate if you are reprocessing historical data. If the ordering of events across streams is undetermined, the join becomes nondeterministic [87], which means you cannot rerun the same job on the same input and necessarily get the same result: the events on the input streams may be interleaved in a different way when you run the job again. In data warehouses, this issue is known as a slowly changing dimension (SCD), and it is often addressed
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