The current docs claim [1]:
"KeyedProcessFunction, as an extension of ProcessFunction, gives access to
the key of timers in its onTimer(...) method."
So, from what it's worth, it seems that if one does not need to query the
current key, wich within a `Keyed(Co)ProcessFunction` can be done like this
```
@Override
public void onTimer(long timestamp, OnTimerContext ctx, Collector<OUT> out)
throws Exception {
K key = ctx.getCurrentKey();
// ...
}
```
, they are mostly interchangeable (???). For instance, if I wanted to
replace an existing `RichCoFlatMapFunction<IN1, IN2, OUT>` that uses keyed
state with a process function, should I use `CoProcessFunction<IN1, IN2,
OUT>` or `KeyedCoProcessFunction<K, IN1, IN2, OUT>`? The type parameters
for the `CoProcessFunction` exactly match those for the `RichCoFlatMap`.
The current docs also claim that `CoProcessFunction` can work with keyed
state [1]:
"The ProcessFunction can be thought of as a FlatMapFunction with access to
keyed state and timers."
Also:
"If you want to access keyed state and timers you have to apply the
ProcessFunction on a keyed stream: `stream.keyBy(...).process(new
MyProcessFunction());`."
so it seems that the natural replacement choice should be the
`CoProcessFunction` unless I'm missing something that strictly requires the
usage of the keyed version (???). However, I've recently commented in [2]
and I got a reply saying that I should go with `KeyedCoProcessFunction` if
I'm using keyed state or timers which is a bit confusing to me. In summary:
- Does replacing a `CoFlatMapFunction` with a `CoProcessFunction` preserve
the original behaviour in presence of keyed state?
- If timers are used later on, does it make any difference if I use
`CoProcessFunction` instead of `KeyedCoProcessFunction`? In my case, I
don't need to explicitly access the current key for anything
(`ctx.getCurrentKey()`).
Thanks in advance!
Salva
---
References
[1]
https://nightlies.apache.org/flink/flink-docs-master/docs/dev/datastream/operators/process_function/#the-keyedprocessfunction
[2]
https://stackoverflow.com/questions/63708216/coprocessfunction-vs-keyedcoprocessfunction-on-connected-keyed-streams/63711885?noredirect=1#comment131747225_63711885
