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From Andrew Xor <andreas.gramme...@gmail.com>
Subject Re: Distribute Spout output among all bolts
Date Thu, 17 Jul 2014 00:10:24 GMT
 Michael,

​ Thanks for the response but I think another problem arises; as ​I just
cooked up a small example the increased number of workers only spawns
mirrors of the topology. This poses a problem for me due to the fact that
my spout reads from a very big file and converts each line into a tuple and
feeds that in the topology. What I wanted to do in the first place is to
actually send each tuple produced to a different subscribed bolt each time
(using Round Robing or smth) so that each one of them got 1/n nth (where n
the number of bolts) of the input stream. If I spawn 2 workers both will
read the same file and emit the same tuples so both topology workers will
produce the same results.

 I wanted to avoid to create a spout that takes a file offset as an input
and wire a lot more stuff than I have to; so I was trying to find a way to
perform what I told you in an elegant and scalable fashion...so far I have
found nil.


On Thu, Jul 17, 2014 at 2:57 AM, Michael Rose <michael@fullcontact.com>
wrote:

> It doesn't say so, but if you have 4 workers, the 4 executors will be
> shared evenly over the 4 workers. Likewise, 16 will partition 4 each. The
> only case where a worker will not get a specific executor is when there are
> less executors than workers (e.g. 8 workers, 4 executors), 4 of the workers
> will receive an executor but the others will not.
>
> It sounds like for your case, shuffle+parallelism is more than sufficient.
>
> Michael Rose (@Xorlev <https://twitter.com/xorlev>)
> Senior Platform Engineer, FullContact <http://www.fullcontact.com/>
> michael@fullcontact.com
>
>
> On Wed, Jul 16, 2014 at 5:53 PM, Andrew Xor <andreas.grammenos@gmail.com>
> wrote:
>
>> Hey Stephen, Michael,
>>
>>  Yea I feared as much... as searching the docs and API did not surface
>> any reliable and elegant way of doing that unless you had a "RouterBolt".
>> If setting the parallelism of a component is enough for load balancing the
>> processes across different machines that are part of the Storm cluster then
>> this would suffice in my use case. Although here
>> <https://storm.incubator.apache.org/documentation/Understanding-the-parallelism-of-a-Storm-topology.html>
>> the documentation says executors are threads and it does not explicitly say
>> anywhere that threads are spawned across different nodes of the cluster...
>> I want to avoid the possibility of these threads only spawning locally and
>> not in a distributed fashion among the cluster nodes..
>>
>> Andrew.
>>
>>
>> On Thu, Jul 17, 2014 at 2:46 AM, Michael Rose <michael@fullcontact.com>
>> wrote:
>>
>>> Maybe we can help with your topology design if you let us know what
>>> you're doing that requires you to shuffle half of the whole stream output
>>> to each of the two different types of bolts.
>>>
>>> If bolt b1 and bolt b2 are both instances of ExampleBolt (and not two
>>> different types) as above, there's no point to doing this. Setting the
>>> parallelism will make sure that data is partitioned across machines (by
>>> default, setting parallelism sets tasks = executors = parallelism).
>>>
>>> Unfortunately, I don't know of any way to do this other than shuffling
>>> the output to a new bolt, e.g. bolt "b0" a 'RouterBolt', then having bolt
>>> b0 round-robin the received tuples between two streams, then have b1 and b2
>>> shuffle over those streams instead.
>>>
>>>
>>>
>>> Michael Rose (@Xorlev <https://twitter.com/xorlev>)
>>> Senior Platform Engineer, FullContact <http://www.fullcontact.com/>
>>> michael@fullcontact.com
>>>
>>>
>>> On Wed, Jul 16, 2014 at 5:40 PM, Andrew Xor <andreas.grammenos@gmail.com
>>> > wrote:
>>>
>>>> ​
>>>> Hi Tomas,
>>>>
>>>>  As I said in my previous mail the grouping is for a bolt *task* not
>>>> for the actual number of spawned bolts; for example let's say you have two
>>>> bolts that have a parallelism hint of 3 and these two bolts are wired to
>>>> the same spout. If you set the bolts as such:
>>>>
>>>> tb.setBolt("b1", new ExampleBolt(), 2 /* p-hint
>>>> */).shuffleGrouping("spout1");
>>>> tb.setBolt("b2", new ExampleBolt(), 2 /* p-hint
>>>> */).shuffleGrouping("spout1");
>>>>
>>>> Then each of the tasks will receive half of the spout tuples but each
>>>> actual spawned bolt will receive all of the tuples emitted from the spout.
>>>> This is more evident if you set up a counter in the bolt counting how many
>>>> tuples if has received and testing this with no parallelism hint as such:
>>>>
>>>> tb.setBolt("b1", new ExampleBolt(),).shuffleGrouping("spout1");
>>>> tb.setBolt("b2", new ExampleBolt()).shuffleGrouping("spout1");
>>>>
>>>> Now you will see that both bolts will receive all tuples emitted by
>>>> spout1.
>>>>
>>>> Hope this helps.
>>>>
>>>> ​
>>>> ​Andrew.​
>>>>
>>>>
>>>> On Thu, Jul 17, 2014 at 2:33 AM, Tomas Mazukna <tomas.mazukna@gmail.com
>>>> > wrote:
>>>>
>>>>> Andrew,
>>>>>
>>>>> when you connect your bolt to your spout you specify the grouping. If
>>>>> you use shuffle grouping then any free bolt gets the tuple - in my
>>>>> experience even in lightly loaded topologies the distribution amongst
bolts
>>>>> is pretty even. If you use all grouping then all bolts receive a copy
of
>>>>> the tuple.
>>>>> Use shuffle grouping and each of your bolts will get about 1/3 of the
>>>>> workload.
>>>>>
>>>>> Tomas
>>>>>
>>>>>
>>>>> On Wed, Jul 16, 2014 at 7:05 PM, Andrew Xor <
>>>>> andreas.grammenos@gmail.com> wrote:
>>>>>
>>>>>> H
>>>>>> ​i,
>>>>>>
>>>>>>  I am trying to distribute the spout output to it's subscribed bolts
>>>>>> evenly; let's say that I have a spout that emits tuples and three
bolts
>>>>>> that are subscribed to it. I want each of the three bolts to receive
1/3
>>>>>> rth of the output (or emit a tuple to each one of these bolts in
turns).
>>>>>> Unfortunately as far as I understand all bolts will receive all of
the
>>>>>> emitted tuples of that particular spout regardless of the grouping
defined
>>>>>> (as grouping from my understanding is for bolt *tasks* not actual
bolts).
>>>>>>
>>>>>>  I've searched a bit and I can't seem to find a way to accomplish
>>>>>> that...​ is there a way to do that or I am searching in vain?
>>>>>>
>>>>>> Thanks.
>>>>>>
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Tomas Mazukna
>>>>> 678-557-3834
>>>>>
>>>>
>>>>
>>>
>>
>

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