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From "Tzu-Li (Gordon) Tai" <tzuli...@gmail.com>
Subject Re: Threading Model for Kinesis
Date Tue, 23 Aug 2016 13:31:57 GMT
Slight misunderstanding here. The one thread per Kafka broker happens
*after* the assignment of Kafka partitions to the source instances. So,
with a total of 10 partitions and 10 source instances, each source instance
will first be assigned 1 partition. Then, each source instance will create
1 thread for every individual broker that holds partitions that the source
instance is assigned. The per-broker threading model of the Kafka consumer
has nothing to do with the initial assignment of partitions to source
instances.

Another example to explain this more clearly:
Say you have 2 Kafka brokers, and each hold 5 partitions, and have source
parallelism 5. Each source instance will still have 2 partitions. If the
2 partitions belong to the same broker, the source instance will have only
1 consuming threads; otherwise if the 2 partitions belong to different
brokers, the source instance will have 2 consuming threads.

Regards,
Gordon


On August 23, 2016 at 8:47:15 PM, Sameer W (sameer@axiomine.com) wrote:

Gordon,

I tried the following with Kafka - 1 Broker but a topic has 10 partitions.
I have a parallelism of 10 defined for the job. I see all my 10
source->Mapper->assignTimestamps receiving and sending data. If there is
only one source instance per broker how does that happen?

Thanks,
Sameer

On Tue, Aug 23, 2016 at 7:17 AM, Tzu-Li (Gordon) Tai <tzulitai@gmail.com>
wrote:

> Hi!
>
> Kinesis shards should be ideally evenly assigned to the source instances.
> So, with your example of source parallelism of 10 and 20 shards, each
> source instance will have 2 shards and will have 2 threads consuming them
> (therefore, not in round robin).
>
> For the Kafka consumer, in the source instances there will be one
> consuming thread per broker, instead of partition. So, if a source instance
> is assigned partitions that happen to be on the same broker, the source
> instance will only create 1 thread to consume all of them.
>
> You are correct that currently the Kafka consumer does not handle
> repartitioning transparently like the Kinesis connector, but we’re working
> on this :)
>
> Regards,
> Gordon
>
> On August 23, 2016 at 6:50:31 PM, Sameer W (sameer@axiomine.com) wrote:
>
> Hi,
>
> The documentation says that there will be one thread per shard. If I my
> streaming job runs with a parallelism of 10 and there are 20 shards, are
> more threads going to be launched within  a task slot running a source
> function to consume the additional shards or will one source function
> instance consume 2 shards in round robin.
>
> Is it any different for Kafka? Based on the documentation my understanding
> is that if there are 10 source function instances and 20 partitions, each
> one will read 2 partitions.
>
> Also if partitions are added to Kafka are they handled by the existing
> streaming job or does it need to be restarted? It appears as though Kinesis
> handles it via the consumer constantly checking for more shards.
>
> Thanks,
> Sameer
>
>

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