#23746: Remedy assertNumQueries dependence on some caches state
-----------------------------------+--------------------------------------
Reporter: wrwrwr | Owner: nobody
Type: Bug | Status: new
Component: Testing framework | Version: master
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by wrwrwr):
* needs_better_patch: => 0
* needs_tests: => 0
* needs_docs: => 0
Old description:
> The `assertNumQueries` manager / method may return different results
> depending on what is in various caches. Consequently, some tests using it
> to rely on test ordering, particularly those that count some content type
> queries. For instance if you [https://code.djangoproject.com/ticket/23742
> run the suite in reverse] you'll see `test_group_permission_performance`
> failing due to `ContentType` being or not being asked about `auth.Group`
> in some preceding test ^[#f1 1]^.
>
> [https://github.com/wrwrwr/django/compare/fix/assert-num-queries-cache-
> dependence The proposed solution] resets "query" caches on entering the
> manager (with a switch to disable it for actual caching tests). After
> introducing the change 10 tests started to fail (`ContentType` cache
> tests and some `prefetch_related` tests), 2 specific workarounds were no
> longer necessary (#17377, #20432) and a failure from
> [https://github.com/django/django/pull/3426 PR 3426] disappeared ^[#f2
> 2]^.
>
> \\
>
> Note to prospective reviewers: Are there any other caches that should be
> cleared besides the `ContentType` and `Site`? Related objects caches
> maybe? Do the affected `prefetch_related` operations actually require
> content type queries? Would it be better to clear all the caches after
> every test case to avoid other kinds of dependencies?
>
> ![1][[=#f1]] What happens in the likewise failing with "--reverse"
> `test_user_permission_performance` is a bit intriguing and probably more
> involved -- two identical content type queries, savepoint, content type
> insertion and a release?
>
> ![2][[=#f2]] Only tested with Python 3.3 / Postgres,
New description:
The `assertNumQueries` manager / method may return different results
depending on what is in various caches. Consequently, some tests using it
rely on test ordering, particularly those that count some content type
queries. For instance if you [https://code.djangoproject.com/ticket/23742
run the suite in reverse] you'll see `test_group_permission_performance`
failing due to `ContentType` being or not being asked about `auth.Group`
in some preceding test ^[#f1 1]^.
[https://github.com/wrwrwr/django/compare/fix/assert-num-queries-cache-
dependence The proposed solution] resets "query" caches on entering the
manager (with a switch to disable it for actual caching tests). After
introducing the change 10 tests started to fail (`ContentType` cache tests
and some `prefetch_related` tests), 2 specific workarounds were no longer
necessary (#17377, #20432) and a failure from
[https://github.com/django/django/pull/3426 PR 3426] disappeared ^[#f2
2]^.
\\
Note to prospective reviewers: Are there any other caches that should be
cleared besides the `ContentType` and `Site`? Related objects caches
maybe? Do the affected `prefetch_related` operations actually require
content type queries? Would it be better to clear all the caches after
every test case to avoid other kinds of dependencies?
![1][[=#f1]] What happens in the likewise failing with "--reverse"
`test_user_permission_performance` is a bit intriguing and probably more
involved -- two identical content type queries, savepoint, content type
insertion and a release?
![2][[=#f2]] Only tested with Python 3.3 / Postgres,
--
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Ticket URL: <https://code.djangoproject.com/ticket/23746#comment:1>
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