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by btown 2150 days ago
As an FYI: Using a gevent monkey patch has been a way to get async Django for years. Overhead is inefficient in CPU cycles and you need to stay away from doing CPU bound things like Numpy manipulations, but for an app server that’s bound by external API call latency, it practically gives infinite concurrency compared to a thread-per-request model. And no need to worry about event queues. You can feel free to synchronously call requests.get with a 10 sec timeout and still serve prod traffic from a small handful of threads. And most days we don’t even worry about async from a coding perspective. Anyone can email me with questions.
2 comments
mgraczyk 2150 days ago
I'd add that crucially, DB ORM operations just work with gevent. It will be a while before async database operations are supported natively by Django. For me that is a complete blocker.
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georgewalker355 2149 days ago
> DB ORM operations just work with gevent

My impression was that django+gevent requires some care for the db part. The psycopg2 docs state, for instance

"Psycopg connections are not green thread safe and can’t be used concurrently by different green threads." [1,2].

In addition, gevent cannot monkey patch psycopg2 code because it is C and not python. This is handled by calling psycopg2.extensions.set_wait_callback() [1,3,4]

I just now realize that you're probably referring to making the ORM itself async capable which is on the roadmap https://code.djangoproject.com/wiki/AsyncProject in which case I totally agree.

[1] https://www.psycopg.org/docs/advanced.html#support-for-corou... [2] https://stackoverflow.com/questions/12650048/how-can-i-pool-... [3] https://github.com/gevent/gevent/blob/master/examples/psycop... [4] https://github.com/psycopg/psycogreen

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btown 2148 days ago
In practice this is just a one-time setup. We use https://github.com/jneight/django-db-geventpool which uses psycogreen under the hood. It isn't perfect (we're currently tracking down some rare cases where connections aren't properly returning to the pool, though we believe this to be error on our side) but it's more than sufficient.

While making the ORM async capable would be great, I'm not sure it will ever make sense to migrate towards sprinkling "async" explicitly across our codebase. We'll see, of course.

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tus88 2150 days ago
gevent should be in core.
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