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July 29, 2014
Luigi
The past, the present, the future

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Section name
Source:
The history
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The long story
builder (2009-2010)
XML madness
Only used for one single project (my Master’s thesis)
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The long story
builder2 (2010-2011)
Everything in Python, but insane amounts of boiler plate
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Why luigi?
We wanted to do everything in Python, not XML
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Source:
How do we use it at Spotify?
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Blah
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The things we got right
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Everything is a directed acyclic graph
Makefile style
Tasks specify what they are dependent on not what other things depend on them
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Do everything in Python
Dependencies often involve algebra hard to express in XML
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Centralized scheduler
Overview of everything that’s currently running/scheduled
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Luigi worker 1 Luigi worker 2
A
B C
A C
F
Luigi central planner

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Trigger jobs locally is trivial
If the only way is to run things remotely, debugging is super hard
Running things locally makes it a lot easier
No messing around with paths and configuration
!
(this has a flip side – more on this later)
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It’s a library more than a framework
Avoid the “Hollywood principle” and make it easy to customize etc
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The hairy parts…
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Execution is tied to scheduling
You can’t run this task “in the cloud” and go away
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Visualization is pretty rudimentary
See how nice Driven looks for instance:
!
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Scheduling isn’t tied to triggering
Need to rely on crontab etc
Could borrow some of the nice parts of Chronos:
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Source:
What are some ideas for the future?
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Separate scheduling and execution
Schedule something to run later/somewhere else
!
Recent baby step towards this is a very simple fix for running modules dynamically:
!
$ luigi --module MyModule MyTask --foo xyz --bar 123!
!
The next step would be to do something like
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$ luigi --module MyModule MyTask --foo xyz --bar 123 --execute-
remotely !
!
A full implementation would include a bunch of command line options to probe status, kill tasks, etc
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Separate scheduling and execution (2)
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Luigi central scheduler
Worker
Worker
Worker
Worker
...

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On-the-fly dependencies
class MyTask(luigi.Task):!
def run(self):!
input = yield OtherTask() # this could replace requires()
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Built in crontab-replacement
@luigi.schedule!
class MyTask(luigi.Task):!
param = luigi.DateParameter(default=datetime.date.today())!
def run(self):!
…!
!
The @luigi.schedule decorator would then
1. Register that my_module.MyTask should be scheduled (by telling the central planner?)
2. Trigger it continuously from somewhere (central planner?)
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ETA for tasks
Using a persistent task history database, you could train a simple k-NN classifier to predict how long
a task will run
Then use this with the dependency graph to predict when any task will finish
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More features in the central planner
Kill a task
Re-launch a task
Launch a new task
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Support for other languages
Luigi is written in Python – but the RPC is language agnostic.
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Happy plumbing!
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Questions?
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