Hey Javier,

Thanks a bunch for your thoughts and insights--much appreciated! Regarding local vs. remote messaging, hopefully local will occur if possible. With what I am seeing scheduler-wise (one Bolt 2, 4 Bolt 1 executors per worker), I am really hopeful I am getting local messaging. I am going to profile it to see the IMAX distruptor  vs Netty communication events to confirm.

Thanks again, Javier!


On Mon, Oct 5, 2015 at 11:38 AM, Javier Gonzalez <jagonzal@gmail.com> wrote:

If you get one bolt2 per worker, it should work as you say. Though I'm not completely sure it's *guaranteed* that every mesage will go local.


On Oct 5, 2015 10:01 AM, "John Yost" <soozandjohnyost@gmail.com> wrote:
Hi Javier,

I apologize, I don't think I am making myself clear. I am attempting to get all the tuples for a given key sent to the same Bolt 2 executor instance. I previously followed the pattern of using fieldsGrouping on Bolt1 as this is a well-established pattern.  However, there are roughly 4 times as many Bolt 1 executors to every Bolt 2 executor, and I was finding the throughput was very low between Bolts 1 and 2.  Once I switched to localOrShuffleGrouping between Bolt 1 and Bolt 2, the throughput tripled. I did this based upon advice from this board to do localOrShuffleGrouping for large fan-in patterns like this (great advice, definitely worked great!).

Unfortunately, this also means that there is no guarantee that all tuples for a given key will be sent to the same Bolt 2. To hopefully get the best of both worlds, I am thinking I can do the fieldsGrouping between KafkaSpout and Bolt 1, and therefore I get the same effect of all tuples for a given key going to the same Bolt 2. Of course, the key (pun intended) is that there is one Bolt 2 per worker, which will ensure all tuples for the same key will go to the same Bolt 1 which will then forward 'em to Bolt 2.

Please confirm if this seems logical and that it should work. I think it should, but I may be missing something.

Thanks! :)


On Mon, Oct 5, 2015 at 9:20 AM, Javier Gonzalez <jagonzal@gmail.com> wrote:

If I'm reading this correctly, I think you're not getting the result you want - having all tuples with a given key processed in the same bolt2 instance.

If you want to have all messages of a given key to be processed in the same Bolt2, you need to do fields grouping from bolt1 to bolt2. By doing fields grouping in the spout-bolt1 hop and shuffle/local in the bolt1-bolt2 hop, you're ensuring that bolt1 instances always see the same key, but is there any guarantee that the bolt2 you want is the nearest/only local bolt available to any given instance of bolt1?


On Oct 5, 2015 7:33 AM, "John Yost" <soozandjohnyost@gmail.com> wrote:
Hi Everyone,

I am currently prototyping FieldsGrouping at the KafkaSpout vs Bolt level. I am curious as to whether anyone else has tried this and, if so, how well this worked.

The reason I am attempting to do FieldsGrouping in the KafkaSpout is that I moved from fieldsGrouping to localOrShuffleGrouping between Bolt 1 and Bolt 2 in my topology due to a 4 to 1 fan in from Bolt 1 to Bolt 2 (for example, 200 Bolt 1 executors and 50 Bolt 2 executors) which was dramatically slowing throughput. It is still highly preferable to do fieldsGrouping one way or another so that I am getting all values for a given key to the same Bolt 2 executor, which is the impetus for attempting to do fieldsGrouping in the KafkaSpout.

If anyone has any thoughts on this approach, I'd very much like to get your thoughts.