Hi, Please take a look for example here: https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/state/state.html#keyed-state <https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/state/state.html#keyed-state> And the example in particular https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/state/state.html#using-managed-keyed-state <https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/state/state.html#using-managed-keyed-state>
The part about "there is a specific key implicitly in context” might be referring to the fact, that for every instance of `CountWindowAverage` that will be running in the cluster, user doesn’t have to set the key context explicility. Flink will set the the key context automatically for the `ValueState<Tuple2<Long, Long>> sum;` before any invocation of `CountWindowAverage#flatMap` method. In other words, one parallel instance of `CountWindowAverage` function, for two consecutive invocations of `CountWindowAverage#flatMap` can be referring to different underlying value of `CountWindowAverage#sum` field. For details you could take a look at `org.apache.flink.streaming.api.operators.AbstractStreamOperator#setKeyContextElement1` method and how it’s being used/implemented. I hope that helps. Piotrek > On 13 Mar 2020, at 08:20, Padarn Wilson <pad...@gmail.com> wrote: > > Hi Users, > > I am trying to understand the details of how some aspects of Flink work. > > While understanding `keyed state` I kept coming up against a claim that > `there is a specific key implicitly in context` I would like to understand > how this works, which I'm guessing means understanding the details of the > runtime context: Is there any documentation or FLIP someone can recommend on > this?
