Hi Aljoscha,
I know it's tricky...
Few weeks ago we decided to implement it without windows, using just
stateful operator and some queues/map per key as state - so yeah, we
tried to imagine how to do this in plain java and one stream ;)
We also process watermarks to evict old events. Fortunately, our streams
are not that big and we can keep all "recent" events in state - without
preaggregation.
Currently we're waiting for some feedback from our client on results -
if it's ok, we'll stick with that, otherwise we'll have to look into it
deeper...
thanks,
maciek
On 25/10/2016 16:41, Aljoscha Krettek wrote:
Hi Maciek,
cases like this, where you essentially want to evict elements that are
older than a certain threshold while keeping a count of those elements
that are not older than that threshold tend to be quite tricky.
In order to start thinking about this, how would you implement this
case in a non-parallel way, in plain Java. You have the stream of
incoming events, they possibly have timestamps, they are possibly not
ordered by that timestamp (this depends on your use case). Now, what
are the algorithms/data structures that could be used for computing
the result that you require?
Cheers,
Aljoscha
On Fri, 23 Sep 2016 at 10:50 Claudia Wegmann <c.wegm...@kasasi.de
<mailto:c.wegm...@kasasi.de>> wrote:
Hey,
I'm no expert at all, but for me this sounds like a use case for
Complex Event Processing (CEP). I don't know if you're aware of
Flinks CEP Library [1, 2]? Maybe that solves your problem of
multiple firings. But best to wait for the experts to answer your
questions on handling state and firing windows :)
Best,
Claudia
[1]: https://flink.apache.org/news/2016/04/06/cep-monitoring.html
[2]:
https://ci.apache.org/projects/flink/flink-docs-master/dev/libs/cep.html
-----Ursprüngliche Nachricht-----
Von: Maciek Próchniak [mailto:m...@touk.pl <mailto:m...@touk.pl>]
Gesendet: Freitag, 23. September 2016 10:36
An: user@flink.apache.org <mailto:user@flink.apache.org>
Betreff: window-like use case
Hi,
in our project we're dealing with a stream of billing events. Each
has customerId and charge amount We want to have a process that
will trigger event (alarm) when sum of charges for customer during
last 4 hours exceeds certain threshold, say
- 10.
The triggered event should contain data from last billing event
(the one that triggered alarm)
One one hand we can implement it as custom state - we'd save
charges (or some precomputed aggregates) from last 4 hours and
trigger event when new one arrives.
OTOH we've been thinking if we can make it easier by using flink
windows.
We tried to model our situation as sliding events (of length
4hours, slide is 1h), have some precomputed aggregate and have a
custom trigger that fires on element when threshold is exceeded.
It kinda works, except for the fact that state is unnecesarily
large, custom trigger is a bit hacky and (worst of all) when event
with charge amount e.g. 20 arrives trigger fires in all slides and
we have duplicated events.
That's why we currently think about implementing it by custom state...
Do you have any other ideas/recommendations how can we handle such
requirement?
thanks,
maciek
