Thanks for the KIP.
A general comment: it seem that we won't need any new `allowedLateness`
parameter because the grace-period is defined on the window itself already?
(On the other hand, if I think about it once more, maybe the
`grace-period` is actually not a property of the window but a property
of the aggregation operator? _thinking_)
From an API flow point of view, option 1 might not be desirable IMHO:
stream
.groupByKey()
.windowBy(TimeWindow.ofSizeNoGrace(...))
.emitFinal()
.count()
The call to `emitFinal(0` seems not to be on the right place for this case?
Option 2 might work (I think we need to discuss a few details of the API
though):
stream
.groupByKey()
.windowBy(
TimeWindow.ofSizeNoGrace(...),
EmitConfig.emitFinal() -- just made this up; it's not in the KIP
)
.count()
I made up the `WindowConfig.emitFinal()` call -- from the KIP it's
unclear what API you have in mind? `EmitFinalConfig` has not public
constructor not any builder method.
For option 3, I am not sure what you really have in mind. Can you given
a concrete example (similar to above) how users would write their code?
Did you consider to actually pass in the `EmitConfig` into the
aggregation operator? In the end, it seems not to be property of the
window definition or windowing step, but a property of the actual operator:
stream
.groupByKey()
.windowBy(
TimeWindow.ofSizeNoGrace(...)
)
.count(EmitConfig.emitFinal())
The API surface area that need to be updated might be larger for this
case though...
-Matthias
On 3/14/22 9:21 PM, Hao Li wrote:
Thanks Guozhang!
1. I agree `EmitConfig` is better than `WindowConfig` and option 2 modifies
less places. What do you think of option 1 which doesn't change the current
`windowedBy` api but configures `EmitConfig` separately. The benefit of
option 1 is if we need to configure something else later, we don't need to
pile them on `windowedBy` but can add separate APIs.
2. I added it to `Stores` mainly to conform to
https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/kstream/internals/TimeWindowedKStreamImpl.java#L227-L231.
But We can also create an internal API to do that without modifying
`Stores`.
Hao
On Mon, Mar 14, 2022 at 7:52 PM Guozhang Wang <wangg...@gmail.com> wrote:
Hello Hao,
Thanks for the proposal, I have some preference among the options here so I
will copy them here:
I'm now thinking if it's better to not add this new config on each of the
Window interfaces, but instead add that at the KGroupedStream#windowedBy
function. Also instead of adding just a boolean flag, maybe we can add a
Configured class like Grouped, Suppressed, etc, e.g. let's call it a
Emitted which for now would just have a single construct as
Emitted.atWindowClose whose semantics is the same as emitFinal == true. I
think the benefits are:
1) you do not need to modify multiple Window classes, but just overload one
windowedBy function with a second param. This is less of a scope for now,
and also more extensible for any future changes.
2) With a config interface, we maintain its extensibility as well as being
able to reuse this Emitted interface for other operators if we wanted to
expand to.
----------------------------
So in general I'm leaning towards option 2). For that, some more detailed
comments:
1) If we want to reuse that config object for other non-window stateful
operations, I think naming it as `EmitConfig` is probably better than
`WindowConfig`.
2) I saw your PR (https://github.com/apache/kafka/pull/11892) that you are
also proposing to add new stores into the public factory Stores, but it's
not included in the KIP. Is that intentional? Personally I think that
although we may eventually want to add a new store type to the public APIs,
for this KIP maybe we do not have to add them but can delay for later after
we've learned the best way to layout. LMK what do you think?
Guozhang
On Fri, Mar 11, 2022 at 2:13 PM Hao Li <h...@confluent.io.invalid> wrote:
Hi Dev team,
I'd like to start a discussion thread on Kafka Streams KIP-825:
https://cwiki.apache.org/confluence/display/KAFKA/KIP-825%3A+introduce+a+new+API+to+control+when+aggregated+results+are+produced
This KIP is aimed to add new APIs to support outputting final aggregated
results for windowed aggregations. I listed several options there and I'm
looking forward to your feedback.
Thanks,
Hao
--
-- Guozhang
