#26306: Memory leak in cached template loader
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Reporter: AlexHill | Owner: nobody
Type: Bug | Status: new
Component: Template system | Version: 1.9
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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There's a pretty serious memory leak in the cached template loader.
Here's a bare-bones project demonstrating the issue:
https://github.com/AlexHill/django_leak_test
To see it happen, run that project under 1.9, hit /safe/ a couple thousand
times, then try the same with /leaky/.
Here's where it happens:
https://github.com/django/django/blob/6679cdd92c71a77f1809c180174de026a6c17918/django/template/loaders/cached.py#L34
I think what's happening is this:
When the exception is raised, it contains a stack trace, which contains
references to a whole lot of stuff up the stack including the
TemplateResponse, the request, etc. That's all cached with the exception.
When it's fetched from the cache and re-raised, Python's exception
handling mechanics result in the exception containing references to the
current stack AND the previous one.
This happens every time it's fetched from cache, so essentially you end up
caching the response and context for every request that produced a
TemplateDoesNotExist error while resolving a template name. In my case,
that's basically every request :)
I think caching and re-raising the actual exception is probably a mistake
- instead, we should cache some sentinel object and raise a new exception
each time.
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Ticket URL: <https://code.djangoproject.com/ticket/26306>
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