kafka-users mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From R Krishna <krishna...@gmail.com>
Subject Re: Questions about single consumer per partition approach
Date Thu, 22 Dec 2016 00:00:59 GMT
Newbie here,
Q2) Think, there is no rebalance if you go with manual partition assignment
(assign(List)
<https://kafka.apache.org/090/javadoc/org/apache/kafka/clients/consumer/KafkaConsumer.html#assign%28java.util.List%29>),
but were you looking for subscribe(List, ConsumerRebalanceListener)
<https://kafka.apache.org/090/javadoc/org/apache/kafka/clients/consumer/KafkaConsumer.html#subscribe%28java.util.List,%20org.apache.kafka.clients.consumer.ConsumerRebalanceListener%29>
to notify on rebalance to cleanup? Don't think you can do both, see here:
https://kafka.apache.org/090/javadoc/org/apache/kafka/clients/consumer/KafkaConsumer.html#assign(java.util.List)
where it mentions that it is not possible to use both manual partition
assignment and group assignment, but, I do wonder what happens if consumers
do different approaches?

Other consumer related exceptions can still happen. And unlike Producer
callback, don't think there is a callback other than try/catch for example
in poll, commit, and other calls. I could not find the best way to
recover/continue from these (non rebalance) exceptions other than retry.

https://kafka.apache.org/090/javadoc/org/apache/kafka/clients/consumer/KafkaConsumer.html#poll(long)
https://kafka.apache.org/090/javadoc/org/apache/kafka/common/errors/package-frame.html


On Wed, Dec 21, 2016 at 2:32 PM, Alexei Levashov <
alexei.levashov@arrayent.com> wrote:

> Thank you Ben, I appreciate your answer.
>
> I AM using the key to send messages from the selected producer to a
> selected partition – Q1 covered.
>
>
> If Q2 seems obscure I could add that I am talking about Java client library
> and basically asked for clarification to the API doc statement that in case
> of manual partition assignment consumer failure doesn’t trigger the
> re-balancing.
>
>  Does the broker register this failure in any shape or form?
>
> Is there a way to notify the application that started consumer thread  (in
> group topic subscription I can subscribe the consumer with a callback that
> IS called on revocation of ownership) about failure of this thread from
> broker point of view?
>
> Thank you
>
> On Wed, Dec 21, 2016 at 6:06 AM, Ben Stopford <ben@confluent.io> wrote:
>
> > Hi Alexi
> >
> > Typically you would use a key to guarantee that messages with the same
> key
> > have a global ordering, rather than using manual assignment. Kafka will
> > send all messages with the same key to the same partition. If you need
> > global ordering, spanning all messages from a single producer, you can
> use
> > a single partition topic. This will limit you to one active consumer per
> > consumer group as the consumer group protocol guarantees that a partition
> > can only be assigned to one consumer, within a group, at one time.
> >
> > B
> >
> > On Wed, Dec 21, 2016 at 4:36 AM Alexei Levashov <
> > alexei.levashov@arrayent.com> wrote:
> >
> > > Hello,
> > > I have a few newbie questions about usage of Kafka as a messaging
> system.
> > > Kafka version - 0.10.1.0.
> > >
> > > 1 - Let's assume that I want to ensure time sequence of events i.e. if
> > > message A from producer was published at time t1 to partition P and
> > message
> > > B from the same producer published to partition P at time t2,
> > > I want to consume message A before message B, provided t1<t2.
> > >
> > > Question1,
> > > Do I have any choice except one consumer per partition?
> > >
> > > 2. - If I have one consumer per partition and use
> > >  consumer.assign(partitionList) call to assign consumer to a partition
> > do I
> > > still need group membership for this single consumer?
> > >      I didn't find clear description what is the protocol of
> interaction
> > > between GroupCoordinator and PartitionLeader
> > > <
> > > https://cwiki.apache.org/confluence/display/KAFKA/
> > Kafka+Client-side+Assignment+Proposal
> > > >
> > > will be in case of  "manual" partition assignment.
> > >      On one hand the API documentation
> > > <
> > > https://kafka.apache.org/0101/javadoc/index.html?org/apache/
> > kafka/clients/consumer/KafkaConsumer.html
> > > >
> > > says
> > > that :
> > >      "Manual partition assignment does not use group coordination, so
> > > consumer failures will not cause assigned partitions to be rebalanced.
> > >       Each consumer acts independently even if it shares a groupId with
> > > another consumer.
> > >       To avoid offset commit conflicts, you should usually ensure that
> > the
> > > groupId is unique for each consumer instance."
> > >
> > >       On the other hand I am still consuming messages in
> > > consumer.poll(timeout) loop and inside this poll() call consumer should
> > > send heartbeats to coordinator.
> > >
> > > Question 2 .
> > >      If consumer doesn't send these heartbeats for [*
> session.timeout.ms
> > > <http://session.timeout.ms>*] period of time  should the partition
> > > ownership be revoked or not?
> > >
> > >      If no - does it mean I have to use homegrown heartbeats for
> consumer
> > > state monitoring? How would the application know that the consumer
> thread
> > > is dead?
> > >      If yes - what callback to notify the application can I use?
> > > ConsumerRebalanceListener is available only for group subscription.
> > >
> > > Thank you.
> > >
> >
>



-- 
Radha Krishna, Proddaturi
253-234-5657

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message