#30451: Add ASGI support to Django.
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Reporter: Andrew Godwin | Owner: Andrew Godwin
Type: New feature | Status: assigned
Component: HTTP handling | Version: master
Severity: Normal | Resolution:
Keywords: asgi | Triage Stage: Accepted
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Ran Benita):
It looks like the patch is going to be merged. I feel like I should at
least point out some downsides before this step is taken. (Note, I am not
a Django dev, just a user).
The patch adds an unconditional asyncio import. It is quite heavy for
something most users won't use at least initially. On my aging laptop:
- Import time: 50ms
- Memory usage: ~5MB
Command for import time: `python3.7 -X importtime -c 'import asyncio' |&
tail -1`
Script for memory usage:
{{{
#!python
from resource import getrusage, RUSAGE_SELF
before = getrusage(RUSAGE_SELF)
import asyncio
after = getrusage(RUSAGE_SELF)
print(f'{after.ru_maxrss - before.ru_maxrss}kb')
}}}
The patch adds 2 dependencies, one direct `asgiref` and one transitive
`async_timeout`.
The patch implements the ASGI specification, but that specification has
not been adopted widely yet and has not been proposed for official status
(that I know of) like WSGI has.
ASGI depends on asyncio, but there are other alternatives worth
considering (like trio and curio). And of course there is gevent which has
been used successfully by many companies (including mine) for async Djagno
for some time.
The patch on its own will run all views in a thread pool
(asgiref.sync_to_async -> loop.run_in_executor -> default
ThreadPoolExecutor). The default number of workers used is the number of
cores * 5, so for example an 8 core will use 40 workers. If postgresql is
used with persistent connections, this is a hazard since postgresql
doesn't like this many connections. So users will need to use a connection
pool, or disable persistent connections.
In my opinion, it would be hasty be merge ASGI support before the overall
plan is decided. If a DEP is later proposed, and rejected (I hope not!),
will it still make sense to have merged this?
--
Ticket URL: <https://code.djangoproject.com/ticket/30451#comment:5>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
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