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From Mark Drago <markdr...@gmail.com>
Subject Re: mapping events to topics
Date Thu, 08 Oct 2015 12:50:19 GMT

Thanks for your reply.  I understand all of the points you've made.  I
think the challenge for us is that we have some consumers that are
interested in messages of one type, but we also have a rules engine that is
checking for events of many types and acting on them.

If we put discrete event types on individual topics:
  * Our rules engine would have to monitor many of these topics (10-20)
  * Other consumers would only see messages they care about

If we put all event types on one topic:
  * Our rules engine only has to monitor one topic
  * Other consumers would parse and then discard the majority of the
messages that they see

Perhaps a better approach would be to have different topics for the
different use cases?  This would be similar to an approach that merges
smaller topics together as needed.  So, each event type would be on its own
topic but then we would put a subset of those messages on another topic
that is destined for the rules engine.  The consumers that only care about
one message type would listen on dedicated topics and the rules engine
would just monitor one topic for all of the events that it cares about.  We
would need to have something moving/creating messages on the rules engine
topic.  We may also run in to another set of problems as the ordering of
messages of different types no longer exists as they're coming from
separate topics.

I'm curious to hear if anyone else has been in a similar situation and had
to make a judgement call about the best approach to take.


I usually approach this questions by looking at possible consumers. You
> usually want each consumer to read from relatively few topics, use most
> of the messages it receives and have fairly cohesive logic for using these
> messages. Signs that things went wrong with too few topics:
> * Consumers that throw away 90% of the messages on topics they read
> * Consumers with gigantic switch statements for handling all the different
> message types they get Signs that you have too many topics:
> * Every consumer needs to read messages from 20 different topics in order
> to construct the objects it actually uses If you ever did data modeling
> for a datawarehouse, this will look a bit
> familiar :) Gwen
> On Tue, Oct 6, 2015 at 4:46 PM, Mark Drago <markdrago@gmail.com> wrote: >
> Hello,
> >
> > At my organization we are already using kafka in a few areas, but we're
> > looking to expand our use and we're struggling with how best to
> distribute
> > our events on to topics.
> >
> > We have on the order of 30 different kinds of events that we'd like to
> > distribute via kafka. We have one or two consumers that have a need to
> > consume many of these types of events (~20 out of the 30) and we have
> other
> > consumers that are only interested in one type of event.
> >
> > We're trying to decide between a model where we have one topic containing
> > many kinds of events or a model where we have many topics each containing
> > one type of event. We have also thought about mixed models where we have
> > one large topic that we later break down in to smaller ones or we have
> many
> > small topics that we later coming in to a large topic.
> >
> > I'm curious to hear about best practices and past experiences from the
> > members of this group. What is the general best practice for reusing
> > topics or creating new ones? What has worked well in the past? What
> > should we be considering while making this decision?
> >
> > Thanks in advance!
> > Mark.

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