A stream processing application in Erlang
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README.md

Breeze

Breeze is a experiment to make a stream processing app in Erlang. The intention is to keep it simple but using Erlang OTP principles with Erlang applications, supervisors and make use of existing behaviours and create new ones when it is suitable. The first versions will be single node without guarantees of processing all events. There might be data loss when a worker crashes.

The processing is started ones the master has been configured with a topology, either by configuring the breeze application with a config file or by calling breeze_master:set_and_start_configuration/1. The topology consists of two types of entities, generating workers and procesing workers, implementing the behaviours breeze_generating_worker and breeze_processing_worker. The names if these will change as soon as I find some better names for them. The generating worker emits Erlang terms from some data source, like a file or twitter stream. The processing worker gets data from generating workers of other processing workers and can emit the same or other Erlang terms.

The topology has the following format:


{Name, WorkerType, BehaviourImplementationModule, NumberOfWorkers, Targets}
Name = atom()
WorkerType = generating_worker | processing_worker
BehaviourImplementationModule = atom()
NumberOfWorkers = integer() | dynamic
Targets = [Target]
Target = {Name, TargetType}
TargetType = all | random | keyhash | dynamic

Where the name is an atom and must be unique in the topology. WorkerType is currently generating_worker or processing_worker. BehaviourImplementationModule is a module implementing the corresponding behaviour for the WorkerType. NumberOfWorkers is an positive integer or the atom dynamic. The Targets is a list of where the worker will emit its tuples and how the data is distributed.

all
the term is sent to all workers
random
the term will be sent to a random worker
keyhash
the term must be a tuple, and it be sent to the worker corresponding to the hash of the first element of the tuple.
dynamic
the term must be a tuple and the tuple will be sent to the worker corresponding to the first element, if it is the first message with this specific value of the first element a new worker will be started. The number of workers for the target must be dynamic.

Below is a example topology where entity "one" is a generating worker and has 1 worker and it send the emitted terms to all workers of entity "two". Entity "two" is a processing worker with 2 workers and it sends its emitted tuples randomly to one of the "three" workers. Entity "three" is also a processing worker and it has 10 workers.

[{breeze,
  [{topology,
    [{one, generating_worker, debug_generating_worker, 1, [{two, all}]},
     {two, processing_worker, debug_processing_worker, 2, [{three, random}]},
     {three, processing_worker, debug_processing_worker, 10, []}]
   }]
 }].

Getting started

git clone https://github.com/daha/breeze-examples.git
cd breeze-examples
rebar get-deps clean compile generate
debug_example/rel/breeze_debug_example/bin/breeze_debug_example console -config `pwd`/debug_example/rel/breeze_debug_example/etc/debug

Design

pw - processing worker
gw - generating worker
wc - worker controller

Diagram over the processes:
1-1: one to one
1-N: one to many

                       +-+
                       | | <- breeze_sup
                      1+-+----------------+
                      / |1  1              \
                     /  |                   \
                  1 /   |1                   \1
                 +-+   +-+                    +-+
       wc_sup -> | |   | | worker_supersup    | | master
               1 +-+   +-+                    +-+
                /       |1
               /        |
            N /         |N
           +-+         +-+
     wc -> | |         | | <- worker_sup
           +-+         +-+
                       1|
                        |
                       N|
                       +-+
                       | | <- pw/gw
                       +-+