#17014: prefetch_related infinite recursion by default managers
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Reporter: akaariai | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 1.3
(models, ORM) | Resolution: fixed
Severity: Normal | Triage Stage: Accepted
Keywords: | Needs documentation: 1
Has patch: 0 | Patch needs improvement: 0
Needs tests: 0 | UI/UX: 0
Easy pickings: 0 |
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Comment (by lukeplant):
I agree that having a production machine taken down is bad - what I'm
saying is that a unit test for this failure might be virtually useless in
stopping that happen, since you would hope that developers would actually
run their code before deploying, and it could come with the risk of taking
down a developer's machine. There are many things for which automated
tests and our testing infrastructure are just not appropriate, and the
Halting Problem tells us that is probably one of them. The only way that
you can have assurance of termination is by analysis.
However, akaariai's solution looks helpful - at least it will provide test
coverage of our recursion detection. I will add a test based on that idea,
thanks.
I'm not so convinced about MAX_PREFETCH_CALLS at this point in time. If
there is a case that we are not covering with the current solution, we
should think about what that is and try to fix it, not paper over it. If
there is definitely a class of cases we cannot fix, we will need a
fallback, but we should go through the thought process. There is also the
problem of setting the value - 100 could be **way** to high to stop some
prefetch_related explosions, depending on the size of the initial query
set and the number of related objects. Is there a better heuristic to
apply?
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Ticket URL: <https://code.djangoproject.com/ticket/17014#comment:6>
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