I have done a lot more reading on this and I really feel pyinotify may not
be required, or we could at least switch to a watchman based service for
simplicity right away. Projects like uwsgi use a stat based approach, as do
most other projects I’ve seen and it appears to work ok for them. watchman
has the advantage of being easier to test, as we can mock the actual
watchman service itself, and it supplies a sane, simple API across all
supported platforms. However it suffers from some limitations I need to
work around.
As an example of a fairly large project I took a look at Sentry. After
running the test suite (and excluding test modules) there are 1,000 loaded
Python modules under sentry.* and 4,000 total entries in sys.modules.
Django accounts for about 600, by far the biggest third party module.
During development it seems likely that it’s not worth polling any builtin
python modules at all, and drastically reducing the polling time for site
packages including Django. That would reduce the number of files to poll by
75%. Perhaps we could even just skip watching site-packages entirely - I
think it’s not very common to edit these in a usual development session,
and if the user finds themselves editing them we could add a flag to
include them in the watch list?
If anyone here has a fairly large Django app they work on could I request
that they run this snippet at some point after it has booted and send me
the output, to see if Sentry is representative?
from collections import Counter
counter = Counter(m.split('.')[0] for m in sys.modules.keys())
total = sum(counter.values())
project_total = counter['PROJECT NAME HERE']
print('Project:', project_total)
print('Total:', total)
print(counter.most_common(20))
Thanks,
Tom
On 8 October 2018 at 12:04:08, Tom Forbes ([email protected]) wrote:
Thanks for the feedback! In the pull request I have re-added support for
pyinotify with tests, it was not as hard to write them as I believed. They
still fail, but I’m working on that!
I’ve found an interesting module confusingly called watchgod. The author
says[1] that with the new os.scandir() method added in python 3.5 a stat
based method can scan a project of 850 files in about 24ms.
While this is watching a single directory tree and not the entirety of
sys.modules I believe we could get similar speedups by being a bit more
intelligent in our approach. For example we really don’t need to stat every
single django.* module every second. I’m guessing that those change very
rarely (unless you’re hacking on Django!), so could maybe stat them every
2–3 seconds or even not at all. We could reduce the stating time on
site-packages modules as well for similar reasons.
If we do this right we could potentially get the overhead down to an
acceptable level that we don’t necessarily need platform specific watchers.
1.
https://github.com/samuelcolvin/watchgod#why-no-inotify–kqueue–fsevent–winapi-support
On 6 October 2018 at 20:56:17, charettes ([email protected]) wrote:
While I understand the complexity of 1. I think shipping a version of
Django without
an equivalent inotify replacement such as watchdog could be problematic.
>From my personal experience when using Django's development server in Docker
containers sharing local volumes installing pyinotify resulted a
significant performance
CPU and I/O improvement.
Simon
Le samedi 6 octobre 2018 15:32:33 UTC-4, Tom Forbes a écrit :
>
> What do we think about removing the pyinotify functionality in the
> autoreloader? For context, if pyinotify is installed (Linux only) the
> autoreloader will attempt to use it to detect file changes over the
> standard polling-based approach. It is generally much more efficient but is
> not cross platform, and is not well documented currently IMO.
>
> I’m hacking away at my attempt at refactoring the autoreloader (
> https://github.com/django/django/pull/8819) and I’ve made some good
> progress but I am worried about the lack of tests for pyinotify (there are
> none!). The current code in master works but it’s really hard to refactor
> in any meaningful way without them. I would very much like to explore
> adding support for watchdog (https://pythonhosted.org/watchdog/) instead
> of pyinotify and these changes I’m working on are a means to that end.
>
> Wwatchdog is a library that wraps efficient platform-specific filesystem
> notifications in cross-platform way, and it includes an inotify
> implementation.
>
> So I think there are three ways forward:
>
> 1.
>
> Spend time and effort adding special tests for PyInotify (testing this
> stuff is not simple, especially with the current code)
> 2.
>
> Remove the functionality with an eye to using something like watchdog
> in the near future
> 3.
>
> Never really touch the autoreloader much (it is some of the oldest and
> nastiest code we have).
>
> Does anyone have any strong opinions on this? Does anyone use the
> pyinotify speedup while developing?
>
> Tom
>
>
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