#jobs - a Job scheduler for load regulation#

Copyright (c) 2010 Erlang Solutions Ltd.

Version: 0.1

Jobs is a job scheduler for load regulation of Erlang applications. It provides a queueing framework where each queue can be configured for throughput rate, credit pool and feedback compensation. Queues can be added and modified at runtime, and customizable "samplers" propagate load status across all nodes in the system.

Specifically, jobs provides three features:

• Job scheduling: A job is scheduled according to certain constraints.
  For instance, you may want to define that no more than 9 jobs of a
  certain type can execute simultaneously and the maximal rate at
  which you can start such jobs are 300 per second.
• Job queueing: When load is higher than the scheduling limits
  additional jobs are queued by the system to be run later when load
  clears. Certain rules govern queues: are they dequeued in FIFO or
  LIFO order? How many jobs can the queue take before it is full? Is
  there a deadline after which jobs should be rejected. When we hit
  the queue limits we reject the job. This provides a feedback
  mechanism on the client of the queue so you can take action.
• Sampling and dampening: Periodic samples of the Erlang VM can
  provide information about the health of the system in general. If we
  have high CPU load or high memory usage, we apply dampening to the
  scheduling rules: we may lower the concurrency count or the rate at
  which we execute jobs. When the health problem clears, we remove the
  dampener and run at full speed again.

Compile and start a shell:

$ rebar get-deps
$ rebar compile
$ erl -pa ebin/ -pa deps/*/ebin -boot start_sasl

Start the jobs application:

1> application:start(jobs).

Paste an example from below into the shell.

jobs:add_queue(three_at_once, [
    {regulators, [{counter, [
                    {name, three_at_once},
                    {limit, 3}
                  ]}]}
]). 
Task = fun(N) ->
    io:format("Task ~p started\n", [N]),
    timer:sleep(2000),
    io:format("Task ~p finished, took 2 seconds.\n", [N])
end,
lists:foreach(fun(N) ->
    spawn( fun() ->
        jobs:run(three_at_once, fun() -> Task(N) end)
    end)        
end, lists:seq(1,10)).

jobs:modify_counter(three_at_once, [{limit,2}]).

jobs:add_queue(three_per_sec, [
    {regulators, [{rate, [
                    {name, three_per_sec},
                    {limit, 3}
                 ]}]}
]). 
Task = fun(N) ->
    io:format("Task ~p started\n", [N]),
    timer:sleep(2000),
    io:format("Task ~p finished, took 2 seconds.\n", [N])
end,
lists:foreach(fun(N) ->
    spawn( fun() ->
        jobs:run(three_per_sec, fun() -> Task(N) end)
    end)        
end, lists:seq(1,10)).

jobs:modify_regulator(rate, three_per_sec, three_per_sec, [{limit, 2}]).

This application requires 'exprecs'. The 'exprecs' module is part of http://github.com/esl/parse_trans

For issues, comments or feedback please [create an issue!] 1

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