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From Jagadish Venkatraman <jagadish1...@gmail.com>
Subject Time-stamp of output from a window operator
Date Thu, 21 Dec 2017 07:10:06 GMT
Hey Flink developers,

I'm trying to understand the behavior of timestamp assignments in Apache
Flink.

Here's my current understanding:

1. A *TimestampAssigner* returns the timestamp of each incoming message,
while a *WatermarkAssigner* emits the watermark for a source. (If
per-operator watermarks are defined, they over-ride the watermarks
generated from the source)
2. For each operator, its watermark is determined as the minimum of all the
incoming watermarks from its prior operators.

I was not sure on how the *timestamp* of the output from an operator is
determined? For instance, let's say, for a pane emitted from an
*EventTimeTumblingWindow*, what is its "timestamp"?

What is the timestamp of a late-arrival?

If I perform another EventTime window, on the output from a previous
window, is it defined?

If there are pointers to the source code I need to look at, I'd appreciate
that as well. Thank you for the help.

-- 
Jagadish V,
Graduate Student,
Department of Computer Science,
Stanford University

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