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For non-keyed data, rescaling semantics is unfortunately a bit fuzzy. For this FLIP, we assume that no data of a given input split can overtake prior data in processing on forward channels. Any fan out or reshuffling will already destroy that ordering guarantee, so we can disregard these cases in this FLIP. If we focus on forward channels, however, we quickly run into situations where the ordering is violated (see Fig. 3).
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Figure 3: Split S1 is moved from source instance I to instance II. If the original operators are
back-pressured, data from the new source instance can overtake the original data.
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