Github user wuchong commented on the issue:
https://github.com/apache/flink/pull/4183
Hi @fhueske , jincheng and me have discussed offline and have an unified
opinion.
We think the approach of window(with custom trigger) + custom operator will
increase the latency when multiple window aggregate is applied. For example,
defer 1 hour to compute with two level window aggregates. The output and
watermark of the first level window have been deferred 1 hour. In fact, the
output is in order now. However, the second window will still defer 1 hour to
compute which result in the result is delayed for two hours.
We think we only need to hold the watermark back at source, then all the
downstream window operators will defer the given offset to compute. And the
end-to-end latency is the given offset.
Therefor, we propose to add a custom operator (to offset the watermark)
after the source (the DataStream in the physical plan tree root). And no custom
trigger needed.
What do you think?
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