In general this sounds like a tremendously useful tool... I'm caused to
wonder, however... what, if any, are the performance impacts?
--
Curtis
On 08/21/2018 08:10 AM, charettes wrote:
Regarding the lazy loading of deferred fields and foreign keys
I wanted to mention I've been working on a third-party application
that allows overriding the default behavior[0].
The project works by tainting objects retrieved from "sealed"
querysets and having fields descriptors lookup whether or not
the object is "sealed" on attribute access and warn the developer
about it if it's the case. Warnings can be elevated to errors
using `filterwarnings` when deemed appropriated (e.g. CI, staging).
It has been an useful tool to assist in figuring out where
`select_related()` and `prefetch_related()` should be used
to adjust complex projects database interactions.
I assume a similar pattern could be used to mark objects retrieved
from `QuerySet.__aiter__` to prevent non-async queries from being
performed on attribute accesses; on `Model._state.async = True`
field descriptors would error out.
Cheers,
Simon
P.-S.
While the project might look complex most of the code takes care
of the delicate tasks of replacing fields descriptors once models
are configured which could be significantly simplified if it was
part of Django core.
[0] https://github.com/charettes/django-seal
Le samedi 9 juin 2018 02:30:59 UTC-4, Josh Smeaton a écrit :
I think most of what you've laid out sounds great and that pursuing
async Django is in the projects best interests. The sync to async
and async to sync wrappers that have come out of channels give me
much more confidence that this project is doable in a reasonable
amount of time with backwards compatibility being preserved.
The only real concern I have at the moment is around your comments
regarding on demand foreign key traversal. If existing code running
synchronously is going to be impacted, that's going to be very
difficult for a lot of people. If it's only asynchronous traversal
that'll have issues, then I have no real concern, as on demand
foreign key fetching is usually a bug anyway.
Having a brief read through the psycopg asynchronous docs[0], it
looks like a number of features will be impossible or troublesome to
use, like transactions, executemany, and named cursors (.iterator()
with server side cursors). We'd also need to investigate how
pgbouncer would work in async mode, as most large sites using
postgres are also using pgbouncer. I would expect support can only
further improve, especially if there is a driver like django
pushing. Fallback would just be to run inside a thread pool though,
so it's not a blocker for the rest of the proposal.
Very exciting times ahead!
[0] http://initd.org/psycopg/docs/advanced.html#asynchronous-support
<http://initd.org/psycopg/docs/advanced.html#asynchronous-support>
On Monday, 4 June 2018 23:18:23 UTC+10, Andrew Godwin wrote:
Hello everyone,
For a while now I have been working on potential plans for
making Django async-capable, and I finally have a plan I am
reasonably happy with and which I think we can actually do.
This proposed roadmap, in its great length, is here:
https://www.aeracode.org/2018/06/04/django-async-roadmap/
<https://www.aeracode.org/2018/06/04/django-async-roadmap/>
I'd like to invite discussion on this potential plan - including:
- Do we think async is worth going after? Note that this is
just async HTTP capability, not WebSockets (that would remain in
Channels)
- Can we do this in a reasonable timeframe? If not, is there a
way around that?
- Are the proposed modifications to how Django runs sensible?
- How should we fund this?
There's many more potential questions, and I really would love
feedback on this. I'm personally pretty convinced that we can
and should do this, but this is a decision we cannot take
lightly, and I would love to hear what you have to say.
Andrew
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