#33700: APPEND_SLASH adds significant latency to all requests not ending in /
(even
if successful)
-------------------------------------+-------------------------------------
Reporter: Anders | Owner: nobody
Kaseorg |
Type: | Status: new
Cleanup/optimization |
Component: HTTP | Version: 4.0
handling |
Severity: Normal | Keywords: CommonMiddleware
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
Originally, `APPEND_SLASH` worked by looking for 404 responses and
replacing them with redirects, so as not to unnecessarily impact the
performance of successful responses. However, commit
9390da7fb6e251eaa9a785692f987296cb14523f in 1.9.5/1.10 changed this to
check `should_redirect_with_slash()` on every request, resulting in a
moderately expensive extra `urlconf` lookup for every request not ending
with `/`, whether or not it succeeds as written.
This performance impact was not considered in the commit message or the
corresponding ticket #26293, so I assume it was an oversight. That ticket
asserted “This doesn't really make sense, since the two settings are not
interdependent”, which is incorrect—performance was the reason for the
interdependence.
The overhead was found to be significant enough in Zulip to merit
[https://github.com/zulip/zulip/commit/229090a3a58de15eb2a76a8e513fa5d9a190170c
subclassing] `CommonMiddleware` to skip it in certain conditions.
Here’s a [https://gist.github.com/andersk/0140318d32f1657ff40cad9e7e353bd2
minimal test project] with an exaggerated number of routes so the overhead
can be easily observed.
{{{
$ ./manage.py runserver
}}}
{{{
$ wrk http://127.0.0.1:8000/url9999
Running 10s test @ http://127.0.0.1:8000/url9999
2 threads and 10 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 232.40ms 73.85ms 570.86ms 69.16%
Req/Sec 21.70 9.47 40.00 63.35%
426 requests in 10.01s, 64.90KB read
Requests/sec: 42.56
Transfer/sec: 6.48KB
$ sed -i 's/# APPEND_SLASH = False/APPEND_SLASH = False/'
slash_test_settings.py
$ wrk http://127.0.0.1:8000/url9999
Running 10s test @ http://127.0.0.1:8000/url9999
2 threads and 10 connections
Thread Stats Avg Stdev Max +/- Stdev
Latency 139.80ms 52.07ms 352.19ms 69.09%
Req/Sec 36.46 12.23 60.00 58.12%
714 requests in 10.01s, 108.79KB read
Requests/sec: 71.32
Transfer/sec: 10.87KB
}}}
--
Ticket URL: <https://code.djangoproject.com/ticket/33700>
Django <https://code.djangoproject.com/>
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