#18785: Extra-Join Regression from ticket #15316
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Reporter: famousactress@… | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.4
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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The change to prevent over-trimming in trim_joins() for
https://code.djangoproject.com/ticket/15316 appears to have introduced
new, unneeded joins (LEFT OUTERs) as a side effect. The result is that in
certain cases Django 1.4+ creates less efficient SQL than Django 1.3.
The following test passes in 1.3.x and fails w/ #15316's change. The
failure is due to a new LEFT OUTER JOIN appearing against Document's
delete_log.
queries/models.py
{{{
class AuditLog(models.Model):
info = models.CharField(max_length=50)
class Person(models.Model):
name = models.CharField(max_length=50)
delete_log = models.ForeignKey(AuditLog)
class Document(models.Model):
status = models.CharField(max_length=50)
delete_log = models.ForeignKey(AuditLog)
person = models.ForeignKey(Person)
}}}
queries/tests:
{{{
class OneFourRegressionProof(unittest.TestCase):
"""
Should evolve this into a better test case that proves something
positive, but for now this
is attempting to provide evidence that for some queries we got less
efficient in Django 1.4
"""
def setUp(self):
pass
def test_it(self):
"""
Ideally, this would only create on INNER join on person.
"""
qs =
Document.objects.exclude(delete_log__isnull=False).filter(status='something',
person__delete_log__isnull=True)
self.assertEquals(1, str(qs.query).count('INNER JOIN'))
self.assertEquals(0, str(qs.query).count('OUTER JOIN'))
}}}
git bisect results:
{{{
(django-base)~/projects/elation/django-fork ((2e56066...)|BISECTING)
philltornroth → git bisect bad
2e56066a5b93b528fbce37285bac591b44bc6ed7 is the first bad commit
commit 2e56066a5b93b528fbce37285bac591b44bc6ed7
Author: Malcolm Tredinnick <malcolm.tredinn...@gmail.com>
Date: Tue Aug 23 03:38:42 2011 +0000
Fixed an isnull=False filtering edge-case. Fixes #15316.
The bulk of this patch is due to some fine analysis from Aleksandra
Sendecka.
git-svn-id: http://code.djangoproject.com/svn/django/trunk@16656
bcc190cf-cafb-0310-a4f2-bffc1f526a37
:100644 100644 5635f2141d5ed22bfcc03df7fd5456a48f7f051e
38c7601579c5b366a5027358a3806b24baeaddfb M AUTHORS
:040000 040000 33a384a63b8e8d7e3b325640339f13a14babc315
fe57cf0e7bc932f15d181d3a186bffe453d6bb2a M django
:040000 040000 afb2570e431195108c3d8b0b634e4b30eac42168
e1213b550270d389ffdca827116642b036855a6b M tests
}}}
It's worth noting that this is effectively an exacerbation of
https://code.djangoproject.com/ticket/10790 . I began the discussion on
that ticket and a patch is starting to take shape, but it looks too
drastic to be a 1.4 merge candidate. I wanted to stand up this related
ticket so that a more surgical fix to 1.4 could be considered, if
reasonable.
Anecdotally, I'm seeing queries in our system where this change added 3-6
new joins, making an upgrade to 1.4 a complete non-starter for us unless
there's a workaround that I haven't turned up yet.
--
Ticket URL: <https://code.djangoproject.com/ticket/18785>
Django <https://code.djangoproject.com/>
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