storm-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Navin Ipe <navin....@searchlighthealth.com>
Subject Re: Understanding parallelism in Storm
Date Thu, 02 Jun 2016 04:55:34 GMT
Absolutely. Thank you very much :-)

On Wed, Jun 1, 2016 at 10:35 PM, Matthias J. Sax <mjsax@apache.org> wrote:

> Hi Navin,
>
> you do not need to worry about concurrency. because each task is
> basically an individual instance of your Spout/Bolt class.
>
> Thus, it cannot happen, that execute() is called on the same spout/bolt
> object by different threads at the same time. It can only happen, that
> execute() is called on different objects at the same time by different
> threads -- but that is no concurrency issue.
>
> Of course, you must not have static member variables in you code! But
> this is a general requirement and not directly related to executor/task
> model.
>
> Hope this answers your question.
>
> -Matthias
>
> On 06/01/2016 10:21 AM, Navin Ipe wrote:
> > Thanks Matthias. I just verified this and found why there's this
> > confusion about tasks.
> >
> > In this case:
> > int BoltParallelism = 3;
> > int BoltTaskParallelism = 2;
> > builder.setBolt("bolt1", new BoltA(), *BoltParallelism*)
> >                 .setNumTasks(*BoltTaskParallelism*)
> >
> > BoltParallelism is indeed the number of executors and
> > BoltTaskParallelism is indeed the number of tasks.
> >
> > BUT
> >
> > int BoltParallelism = 3;
> > builder.setBolt("bolt1", new BoltA(), *BoltParallelism*)
> >
> > When you don't specify setNumTasks, Storm creates BoltParallelism number
> > of tasks and creates BoltParallelism number of executors as well.
> >
> > *To your reply of "/No. All executors run in parallel/":*
> > When I have 3 tasks and 3 executors, I won't have to worry about
> > concurrency inside the Bolt, right? Because every Bolt instance is being
> > run in a separate thread, so all their member variables and functions
> > are specific to the executor.
> > Also, even if I have 3 tasks and 1 executor, every task is going to be
> > run one after the other by the executor, so there's no worry about
> > concurrency here either.
> >
> > So in what situation would I have to worry about concurrency? AFAIK,
> > even in a single bolt, the execute() function has to complete before the
> > same execute() is invoked again.
> >
> >
> > On Tue, May 17, 2016 at 12:54 AM, Matthias J. Sax <mjsax@apache.org
> > <mailto:mjsax@apache.org>> wrote:
> >
> >     Answers inline.
> >
> >     I guess you are not aware, that a worker run other thread next to the
> >     executors, too. For example, there are two threads (one for input;
> one
> >     for output), that work as "dispatcher" for incoming messages. There
> is a
> >     global input queue, and the dispatcher "forwards" incoming messages
> to
> >     the individual tasks queues such that the executors can all work in
> >     parallel. Same for output. Executors write into own output queues
> and a
> >     single "output thread" reads the data from there and take care of
> >     network transfer to downstream bolts.
> >
> >     -Matthias
> >
> >     On 05/16/2016 06:24 PM, Navin Ipe wrote:
> >     > Err...guys....I appreciate the ongoing discussion, but the original
> >     > question remains unanswered. The one I've asked at the very
> beginning of
> >     > this conversation. Some help would be appreciated.
> >     > Referring to the code I posted and as per Nathan's answer, you say
> that
> >     > int *BoltParallelism* actually represents the tasks
> >
> >     No. *BoltParallslim* is the number of executor threads.
> >
> >     which are the number
> >     > of instances of Bolts/Spouts? And BoltTaskParallelism is the
> number of
> >     > executors (OS threads)?
> >
> >     No. This is the number of tasks.
> >
> >     > If that's the case, then execute() will get called only after the
> >     > previous execute() call of a Bolt has completed. And nextTuple()
> will
> >     > get called only after the previous nextTuple() of a Spout has
> completed.
> >
> >     For a single executor, yes.
> >
> >     > That's a bit reassuring, since now one does not have to cater to
> >     > multithreading within a Spout/Bolt.
> >
> >     No. All executors run in parallel.
> >
> >     >
> >     >
> >     > On Mon, May 16, 2016 at 7:07 PM, Matthias J. Sax <mjsax@apache.org
> <mailto:mjsax@apache.org>
> >     > <mailto:mjsax@apache.org <mailto:mjsax@apache.org>>> wrote:
> >     >
> >     >     Hi,
> >     >
> >     >
> >     >     So this is not correct:
> >     >     > and
> >     >     > the Bolt creates a task for processing each incoming Tuple.
> >     >
> >     >     Storm create exactly *BoltTaskParallelism* tasks and assigns
> incoming
> >     >     messages to tasks (according to the used connection pattern --
> shuffle,
> >     >     fieldsGrouping etc).
> >     >
> >     >     Futhermore:
> >     >
> >     >     > If there
> >     >     > are not enough tasks, then the excess Tuples are made to
> wait in a
> >     >     > queue of the executor.
> >     >
> >     >     No. There is no thing as "not enough tasks". Each task has its
> own input
> >     >     queue/buffer and tuple are stored there.
> >     >
> >     >     The executor threads process one or multiple tasks. Thus, if a
> task is
> >     >     currently "on hold", new tuples are just added to the task's
> input
> >     >     queue. If an executor picks up on of its tasks for processing,
> the
> >     >     buffered tuples of the task are processed.
> >     >
> >     >
> >     >     -Matthias
> >     >
> >     >     On 05/16/2016 09:07 AM, Adrien Carreira wrote:
> >     >     > +1
> >     >     >
> >     >     > 2016-05-16 6:40 GMT+02:00 Navin Ipe <
> navin.ipe@searchlighthealth.com
> >     <mailto:navin.ipe@searchlighthealth.com>
> >     <mailto:navin.ipe@searchlighthealth.com
> >     <mailto:navin.ipe@searchlighthealth.com>>
> >     >     > <mailto:navin.ipe@searchlighthealth.com
> >     <mailto:navin.ipe@searchlighthealth.com>
> >     >     <mailto:navin.ipe@searchlighthealth.com
> >     <mailto:navin.ipe@searchlighthealth.com>>>>:
> >     >     >
> >     >     >     Hi,
> >     >     >
> >     >     >     I've seen the explanations
> >     >     >
> >     >
> >     <
> http://www.michael-noll.com/blog/2012/10/16/understanding-the-parallelism-of-a-storm-topology/
> >,
> >     >     >     but none of them explain it in terms of what I see in
> >     the code. This
> >     >     >     is what I understood:
> >     >     >
> >     >     >     int BoltParallelism = 3;
> >     >     >     int BoltTaskParallelism = 2;
> >     >     >     builder.setBolt("bolt1", new BoltA(), *BoltParallelism*)
> >     >     >                     .setNumTasks(*BoltTaskParallelism*)
> >     >     >
> >     >     >     BoltParallelism creates 3 instances of BoltA. These are
> the
> >     >     executors.
> >     >     >     BoltTaskParallelism allows Tuples to come into BoltA very
> >     >     fast, and
> >     >     >     the Bolt creates a task for processing each incoming
> >     Tuple. If
> >     >     there
> >     >     >     are not enough tasks, then the excess Tuples are made to
> >     wait in a
> >     >     >     queue of the executor.
> >     >     >
> >     >     >     Strange thing is that the explanation says the tasks are
> >     run in a
> >     >     >     single thread, so obviously I misunderstood something.
> >     Could you
> >     >     >     help me understand it?
> >     >     >
> >     >     >     --
> >     >     >     Regards,
> >     >     >     Navin
> >     >     >
> >     >     >
> >     >
> >     >
> >     >
> >     >
> >     > --
> >     > Regards,
> >     > Navin
> >
> >
> >
> >
> > --
> > Regards,
> > Navin
>
>


-- 
Regards,
Navin

Mime
View raw message