Direct grouping as it is shown in storm docs, means that you have to have a specific task id and use "direct streams" which is error prone, probably increase latency and might introduce redundancy problems as the producer of tuple needs to know the id of the task the tuple will have to go; so imagine a scenario where the receiving task fails for some reason and the producer can't relay the tuples unless it received the re-spawned task's id.
Hope this helps. Kindly yours, Andrew Grammenos -- PGP PKey -- <https://www.dropbox.com/s/2kcxe59zsi9nrdt/pgpsig.txt> https://www.dropbox.com/s/ei2nqsen641daei/pgpsig.txt On Thu, Jul 16, 2015 at 11:24 PM, Nick R. Katsipoulakis < [email protected]> wrote: > Hello again, > > Nathan, I am using direct-grouping because the application I am working on > has to be able to send tuples directly to specific tasks. In general > control the data flow. Can you please explain to me why you would not > recommend direct grouping? Is there any particular reason in the > architecture of Storm? > > Thanks, > Nick > > 2015-07-16 16:20 GMT-04:00 Nathan Leung <[email protected]>: > >> I would not recommend direct grouping unless you have a good reason for >> it. Shuffle grouping is essentially random with even distribution which >> makes it easier to characterize its performance. Local or shuffle grouping >> stays in process so generally it will be faster. However you have to be >> careful in certain cases to avoid task starvation (e.g. you have kafka >> spout with 1 partition on the topic and 1 spout task, feeding 10 bolt "A" >> tasks in 10 worker processes). Direct grouping depends on your code (i.e. >> you can create hotspots), fields grouping depends on your key distribution, >> etc. >> >> On Thu, Jul 16, 2015 at 3:50 PM, Nick R. Katsipoulakis < >> [email protected]> wrote: >> >>> Hello all, >>> >>> I have two questions: >>> >>> 1) How do you exactly measure latency? I am doing the same thing and I >>> have a problem getting the exact milliseconds of latency (mainly because of >>> clock drifting). >>> 2) (to Nathan) Is there a difference in speeds among different >>> groupings? For instance, is shuffle faster than direct grouping? >>> >>> Thanks, >>> Nick >>> >>> 2015-07-15 17:37 GMT-04:00 Nathan Leung <[email protected]>: >>> >>>> Two things. Your math may be off depending on parallelism. One emit >>>> from A becomes 100 emitted from C, and you are joining all of them. >>>> >>>> Second, try the default number of ackers (one per worker). All your ack >>>> traffic is going to a single task. >>>> >>>> Also you can try local or shuffle grouping if possible to reduce >>>> network transfers. >>>> On Jul 15, 2015 12:45 PM, "Kashyap Mhaisekar" <[email protected]> >>>> wrote: >>>> >>>>> Hi, >>>>> We are attempting a real-time distributed computing using storm and >>>>> the solution has only one problem - inter bolt latency on same >>>>> machine or across machines ranges between 2 - 250 ms. I am not able to >>>>> figure out why. Network latency is under 0.5 ms. By latency, I mean >>>>> the time between an emit of one bolt/spout to getting the message in >>>>> execute() of next bolt. >>>>> >>>>> I have a topology like the below - >>>>> A (Spout) ->(Emits a number say 1000) -> B (bolt) [Receives this >>>>> number and divides this into 10 emits of 100 each) -> C (bolt) [Recieves >>>>> these emits and divides this to 10 emits of 10 numbers) -> D (bolt) [Does >>>>> some computation on the number and emits one message] -> E (bolt) >>>>> [Aggregates all the data and confirms if all the 1000 messages are >>>>> processed) >>>>> >>>>> Every bolt takes under 3 msec to complete and as a result, I estimated >>>>> that the end to end processing for 1000 takes not more than 50 msec >>>>> including any latencies. >>>>> >>>>> *Observations* >>>>> 1. The end to end time from Spout A to Bolt E takes 200 msec to 3 >>>>> seconds. My estimate was under 50 msec given that each bolt and spout take >>>>> under 3 msec to execute including any latencies. >>>>> 2. I noticed that the most of the time is spent between Emit from a >>>>> Spout/Bolt and execute() of the consuming bolt. >>>>> 3. Network latency is under 0.5 msec. >>>>> >>>>> I am not able to figure out why it takes so much time between a >>>>> spout/bolt to next bolt. I understand that the spout/bolt buffers the data >>>>> into a queue and then the subsequent bolt consumes from there. >>>>> >>>>> *Infrastructure* >>>>> 1. 5 VMs with 4 CPU and 8 GB ram. Workers are with 1024 MB and there >>>>> are 20 workers overall. >>>>> >>>>> *Test* >>>>> 1. The test was done with 25 messages to the spout => 25 messages are >>>>> sent to spout in a span of 5 seconds. >>>>> >>>>> *Config values* >>>>> Config config = new Config(); >>>>> config.put(Config.TOPOLOGY_WORKERS, Integer.parseInt(20)); >>>>> config.put(Config.TOPOLOGY_EXECUTOR_RECEIVE_BUFFER_SIZE, 16384); >>>>> config.put(Config.TOPOLOGY_EXECUTOR_SEND_BUFFER_SIZE, 16384); >>>>> config.put(Config.TOPOLOGY_ACKER_EXECUTORS, 1); >>>>> config.put(Config.TOPOLOGY_RECEIVER_BUFFER_SIZE, 8); >>>>> config.put(Config.TOPOLOGY_TRANSFER_BUFFER_SIZE, 64); >>>>> >>>>> Please let me know if you have encountered similar issues and any >>>>> steps you have taken to mitigate the time taken between spout/bolt and >>>>> another bolt. >>>>> >>>>> Thanks >>>>> Kashyap >>>>> >>>> >>> >>> >>> -- >>> Nikolaos Romanos Katsipoulakis, >>> University of Pittsburgh, PhD candidate >>> >> >> > > > -- > Nikolaos Romanos Katsipoulakis, > University of Pittsburgh, PhD candidate >
