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Should streamz handle exceptions?

Aperta
#86 7 commenti 0 reazioni 0 assegnatari Vedi su GitHub

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Valutazione

Difficoltà
5/5
Tempo stimato
Più di una settimana
Idoneità per principianti
20/100
Tipo di issue
Funzionalità
Chiarezza
Da chiarire
Stato di attività
Ferma
Stack tecnologico
python
Ambito
stream-processing

Direzione di ricerca

Start by tracing how exceptions move through map, filter, zip, and emit, and review the existing subclassed-module approach described in the issue. Define a consistent exception-handling contract for stream operators, including how bad data is propagated or reported, then document the behavior and cover the affected paths with tests.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

What do we do when a stream receives bad data that causes an exception to be raised. For ex:

def foo(x):
    if x is None:
        raise Exception
    else:
        return x + 1
s = Stream()
s2 = s.map(foo)
s3.sink(print)

s.emit(1)
s.emit(None)
s.emit(2)

Here, foo is a point of vulnerability in the stream, where it may or may not cause the whole stream architecture to halt.

Is it worth trying to incorporate some quiet exception handling? I am not sure exactly how to tackle this so I'm being a little vague at this point. I can think of many ways of doing this. Here are a few:

  1. Catch the exceptions and emit them somehow (will require defining a data type). We can also not emit (and perhaps sink errors to a global list) but this may cause unintended synchronization consequences to the user.
  2. catch the exceptions in s.emit. Note that in this case catching the exception may be harder to find

I'll think about it, but I would like to hear opinions from @mrocklin and @CJ-Wright (who has already handled this in his streams extension). My current method is to wrap all mapped functions to look for exceptions, and return a document that flags the document as having encountered an exception. This works in my subclassed module only though. It would be nice to unify this I think.

(Note: exceptions can occur not just in map but other things like filter etc. Other modules like zip may also want to be exception aware, that something passing through is bad data, and pass this on etc.)

Lingua principale
Python
Stelle
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Merge medio
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PR unite (30g)
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