#13871: contrib.admin:list_editable - ForeignKey performance is O(m*n)
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Reporter: chadc | Owner:
nobody
Status: new | Milestone:
Component: django.contrib.admin | Version:
1.2
Keywords: list_editable, admin, ForeignKey, admin efficiency | Stage:
Unreviewed
Has_patch: 0 |
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'''Overview'''
Including ForeignKey fields in list_editable results in m*n database
queries where m is the number of ForeignKey fields in list_editable and n
is the number of rows in the changelist.
'''Description'''
I have been experiencing poor performance with the admin changelist when
list_editable includes ForeignKey fields. In particular, rendering the
changelist requires O(m*n) database queries where m is the number of
ForeignKey fields included in list_editable and n is the number of rows in
the changelist. The problem, as I understand it, stems from the fact that
the choices for the ForeignKey widgets are not cached. So, when each
ForeignKey widget is rendered, it queries the database to retrieve the
list of possible values.
My solution to this problem has been to override the Select widget with a
CachedSelect widget in the admin model. However, as Jeremy Dunck noted in
django-developers (link below), this may stem from a more general problem
with ModelFormSet. I have ticketed this under contrib.admin for now, but I
hope that Jeremy will update it as any larger issues become clear.
'''Example'''
{{{
class Host(models.Model):
name = models.CharField(max_length=128, unique=True)
class Account(models.Model):
host = models.ForeignKey(Host, related_name="accounts")
name = models.CharField(max_length=128)
class AccountAdmin(admin.ModelAdmin):
list_display = ('name', 'host')
list_editable = ('host',)
list_per_page = 25
admin.site.register(Account, AccountAdmin)
}}}
Rendering the ForeignKey widgets in this example requires n*m=25*1=25
database queries:
SELECT "hosts_host"."id", "hosts_host"."name" FROM "hosts_host" ORDER BY
"hosts_host"."name" ASC
Total time: 330 ms
Numer of queries: 25
'''Related Links'''
django-developers: http://groups.google.ca/group/django-
developers/browse_thread/thread/76066baed6ba70dc
django-users: http://groups.google.ca/group/django-
users/browse_thread/thread/7b63fd40c891ec19
--
Ticket URL: <http://code.djangoproject.com/ticket/13871>
Django <http://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
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