#34597: Django ORM query SQL generation changed (and is apparently a lot slower)
-------------------------------------+-------------------------------------
Reporter: Lorand | Owner: nobody
Varga |
Type: Bug | Status: new
Component: Database | Version: 4.2
layer (models, ORM) |
Severity: Release | Keywords:
blocker |
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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My app has 2 models (making things simple so debugging is easier):
{{{
class Blog(models.Model):
title = models.CharField(max_length=60, blank=True)
is_published = models.BooleanField(default=generate_random_bool,
db_index=True)
class Translation(models.Model):
blog = models.ForeignKey('Blog', on_delete=models.CASCADE,
related_name='translation')
}}}
There is a reverse foreign key relation between translation and Blog. Also
a blog can have multiple translations (or none).
I have this code block:
{{{
from django.db.models import Q
qs = Blog.objects.filter(Q(is_published=True) & ~Q(translation=None))
print(qs.query)
}}}
django 2.2 ORM generates this output:
{{{
SELECT
"blog"."id",
"blog"."title",
"blog"."is_published"
FROM
"blog"
WHERE
(
"blog"."is_published" = True
AND NOT (
"blog"."id" IN (
SELECT
U0."id"
FROM
"blog" U0
LEFT OUTER JOIN "translation" U1 ON (U0."id" = U1."blog_id")
WHERE
(
U1."id" IS NULL
AND U0."id" = ("blog"."id")
)
)
)
)
}}}
For the same code block the django 3.2+ ORM (tried also the latest version
of django 4.2.1) it generates:
{{{
SELECT
"blog"."id",
"blog"."title",
"blog"."is_published"
FROM
"blog"
WHERE
(
"blog"."is_published"
AND NOT (
EXISTS(
SELECT
(1) AS "a"
FROM
"blog" U0
LEFT OUTER JOIN "translation" U1 ON (U0."id" = U1."blog_id")
WHERE
(
U1."id" IS NULL
AND U0."id" = "blog"."id"
AND "blog"."id" = "blog"."id"
)
LIMIT
1
)
)
)
}}}
which is a whole lot slower (at least on the same postgresql 13.7
instance).
The django 2.2 version executes in a couple of seconds while the newer
version executes in half an hour.
I think (but am not completely sure, might be terribly wrong) that the
issue was introduced here:
https://github.com/django/django/pull/13300/files
Environment:
asgiref==3.7.1
backports.zoneinfo==0.2.1
Django==3.2.19
model-bakery==1.11.0
psycopg2-binary==2.8.6
pytz==2023.3
sqlparse==0.4.4
typing_extensions==4.6.1
Db environment:
PostgreSQL 13.7 on aarch64-unknown-linux-gnu, compiled by gcc (GCC) 7.3.1
20180712 (Red Hat 7.3.1-6), 64-bit
Bug does not manifest in django 2.2.12.
Bug manifests in django 3.2 and django 4.2.
--
Ticket URL: <https://code.djangoproject.com/ticket/34597>
Django <https://code.djangoproject.com/>
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