#29943: Slow admin chanelist query (because of adding `pk` to ordering)
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Reporter: Taha Jahangir | Owner: nobody
Type: Bug | Status: new
Component: contrib.admin | Version: master
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 1
UI/UX: 0 |
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Consider a simple model with this definition for model and admin:
{{{
class MyModel(models.Model):
class Meta:
ordering = ('-created',)
created = models.DateTimeField(default=now, db_index=True)
message = models.CharField(max_length=20)
@admin.register(MyModel)
class MyModelAdmin(admin.ModelAdmin):
pass
}}}
We created a model with the **indexed** `created` field, and `ordering`
field set to it . It should works nicely. But if the tables go large, the
listing will be slow, because the generated query is like:
{{{
SELECT "myapp_mymodel"."id", "myapp_mymodel"."created",
"myapp_mymodel"."message" FROM "myapp_mymodel" ORDER BY
"myapp_mymodel"."created" DESC, "myapp_mymodel"."id" DESC LIMIT 100;
}}}
And the database (in my case, postgresql) **WILL NOT** use the `created`
index and the query becomes very slow.
I treat this as a bug, because the default behavior of admin module is not
sensible (and not documented), and will result in performance bug in
normal setups , and it cannot be changed in a simple manner (without
copying/monkey-patching of `ChangeList.get_ordering` method).
--
Ticket URL: <https://code.djangoproject.com/ticket/29943>
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