Just to say that I've reopened the original issue in question as it's clear now this needs to be fixed. I won't be able to get to writing a fix for a bit, though, so if someone else wants to they should.
Andrew On Tue, Aug 28, 2018 at 5:41 AM John Obelenus <jobele...@gmail.com> wrote: > Just finished reading both bug reports and I see the file loader lookup in > whitenoise. This explains a lot actually. We are still on Channels 1, and > when we tried an upgrade to Channels 2, but encountered terrible > performance at load and had to undo it. > > On Tuesday, August 28, 2018 at 8:00:17 AM UTC-4, John Obelenus wrote: >> >> Can I ask a dumb question? Why did you only discover this with adding >> Whitenoise, and not the default/common middleware stack that comes in >> django? Asking that question in another way: What is specific to whitenoise >> that this constant loading of middleware causes such a perf hit? This >> question in no way implies this should not be fixed, its just my curiosity >> (I'm in the exact same situation of running channels and whitenoise) >> >> On Monday, August 27, 2018 at 12:46:15 PM UTC-4, Carl-Philip Majgaard >> wrote: >>> >>> After some digging, I was able to find the reason for why adding the >>> Whitenoise middleware to my Channels-enabled project was causing a massive >>> performance drop. >>> >>> >>> It appears that for every inbound HTTP request, Channels initializes a >>> new AsgiHandler. In turn, this means that the entire middleware stack is >>> being loaded for every HTTP request. See below: >>> >>> >>> https://github.com/django/channels/blob/master/channels/routing.py#L45-L62 >>> >>> https://github.com/django/channels/blob/master/channels/http.py#L157-L183 >>> >>> >>> This has two consequences: >>> >>> 1. Channels is causing middleware to fall out of conformity with >>> Django documentation, which states that middleware’s __init__() is only >>> called *once*, on server startup. >>> 2. Any middleware which performs more-than-trivial work in its >>> __init__() causes massive latency on any incoming request. >>> >>> >>> The issue was diagnosed in: >>> >>> https://github.com/django/channels/issues/1099 >>> >>> https://github.com/django/channels/issues/1121 >>> >>> >>> In response to the diagnosis in django/channels #1121, Andrew Godwin >>> says: >>> >>> Hmm, ASGI middleware is loaded every request (#1099 >>> <https://github.com/django/channels/issues/1099>) so it's quite >>> possible I made the same mistake with the Django middleware as the handler >>> is loaded every request too. If so, someone should be able to patch that >>> quite easily. >>> >>> >>> However, I feel that a patch to this issue would be non-trivial to >>> create. >>> >>> >>> If the AsgiHandler is refactored such that it receives *scope* upon >>> __call__() rather than on __init__() (and is only initialized once)*, *it >>> no longer conforms to the tests defined in >>> https://github.com/django/asgiref/blob/master/asgiref/testing.py#L17, >>> as they require passing scope for initialization. Thus, the AsgiHandler >>> would no longer fit the shape of an Asgi Application. >>> >>> >>> I would attempt a fix for this, but I am unsure of how to approach it >>> given the constraints of the problem. >>> >>> Perhaps someone more knowledgeable about Channels could chime in with >>> their $0.02? I would love to devote some time to fixing this, but need some >>> input before I do. >>> >>> >>> >>> -- > You received this message because you are subscribed to the Google Groups > "Django developers (Contributions to Django itself)" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to django-developers+unsubscr...@googlegroups.com. > To post to this group, send email to django-developers@googlegroups.com. > Visit this group at https://groups.google.com/group/django-developers. > To view this discussion on the web visit > https://groups.google.com/d/msgid/django-developers/998d7855-152e-4bc1-b2f2-8fd0f80099b4%40googlegroups.com > <https://groups.google.com/d/msgid/django-developers/998d7855-152e-4bc1-b2f2-8fd0f80099b4%40googlegroups.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-developers+unsubscr...@googlegroups.com. To post to this group, send email to django-developers@googlegroups.com. Visit this group at https://groups.google.com/group/django-developers. To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/CAFwN1uqyC6a1p0pKRv%2Brh9ZTwYyyu_Q4S7OgvSOfghdSdqCZng%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
