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From "Matthias J. Sax" <matth...@confluent.io>
Subject Re: Adding topics to KafkaStreams after ingestion has been started?
Date Sat, 03 Dec 2016 00:27:30 GMT
If you keep old topics that are completely processed, there would be
increasing overhead, because Streams would try to read from those topics
as long as they exist. Thus, more fetch request will be sent to those
more topics over time, while most fetch request will return without any
new data (as those old topic do not have new data)

If you delete completely processed topics, there will be no overhead.


On 12/2/16 3:58 PM, Ali Akhtar wrote:
> Hey Matthias,
> So I have a scenario where I need to batch a group of messages together.
> I'm considering creating a new topic for each batch that arrives, i.e
> batch_<some_id>.
> Each batch_<id> topic will have a finite number of messages, and then it
> will remain empty. Essentially these will be throwaway topics.
> Is there any overhead to there being a lot of these topics, and having a
> listener for batch_.* , or is this effectively like having one listener for
> one topic?
> On Fri, Dec 2, 2016 at 11:09 PM, Matthias J. Sax <matthias@confluent.io>
> wrote:
>> 1) There will be once consumer per thread. The number of thread is
>> defined by the number of instances you start and how many threads you
>> configure for each instance via StreamConfig parameter
>> NUM_STREAM_THREADS_CONFIG. Thus, you control this completely by yourself.
>> Depending on the number to partitions in your topics, each thread will
>> process one or multiple partitions. As a partition will be processed by
>> exactly one thread, the overall number of partitions over all you input
>> topics limits your max number of thread (if you have more threads, those
>> will just be idle)
>> 2) Thus, there should be no performance issues. Furthermore, if you
>> create new topic while you application is running -- and if this might
>> overload you current application -- you can always start new instances
>> an scale-out you application dynamically -- Kafka Streams is fully elastic.
>> Have a look here for more details:
>> http://docs.confluent.io/current/streams/architecture.html
>> -Matthias
>> On 12/2/16 6:23 AM, Ali Akhtar wrote:
>>> That's pretty useful to know - thanks.
>>> 1) If I listened too foo-.*, and there were 5 foo topics created after
>>> kafka streaming was running: foo1, foo2, foo3, foo4, foo5, will this
>> create
>>> 5 consumers / threads / instances, or will it be just 1 instance that
>>> receives the messages for all of those topics?
>>> 2) Will this cause issues performance issues if i had a lot of throwaway
>>> foo topics being created, or will this scale?
>>> On Fri, Dec 2, 2016 at 7:17 PM, Damian Guy <damian.guy@gmail.com> wrote:
>>>> Hi Ali,
>>>> The only way KafkaStreams will process new topics after start is if the
>>>> original stream was defined with a regular expression, i.e,
>>>> kafka.stream(Pattern.compile("foo-.*");
>>>> If any new topics are added after start that match the pattern, then
>> they
>>>> will also be consumed.
>>>> Thanks,
>>>> Damian
>>>> On Fri, 2 Dec 2016 at 13:13 Ali Akhtar <ali.rac200@gmail.com> wrote:
>>>>> Heya,
>>>>> Normally, you add your topics and their callbacks to a StreamBuilder,
>> and
>>>>> then call KafkaStreams.start() to start ingesting those topics.
>>>>> Is it possible to add a new topic to the StreamBuilder, and start
>>>> ingesting
>>>>> that as well, after KafkaStreams.start() has been called?
>>>>> Thanks.

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