Re: contrib.admin:list_editable - ForeignKey Performance is O(m*n)?
On Wed, Jun 30, 2010 at 2:04 AM, chadc wrote: ... > 3. Overriding the ForeignKey widget with a custom CachedSelect widget. > ... > > PS: For the sake of posterity, I have included the code for my > CachedSelect widget. Yes, I am aware that using regular expressions to > parse the key is a nasty hack. If you have any better ideas, please > let me know! For clarity of what's going on here, would you mind posting an example model? -- You received this message because you are subscribed to the Google Groups "Django developers" group. To post to this group, send email to django-develop...@googlegroups.com. To unsubscribe from this group, send email to django-developers+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-developers?hl=en.
Re: contrib.admin:list_editable - ForeignKey Performance is O(m*n)?
On Tue, Jun 29, 2010 at 6:04 PM, chadc wrote:
> Hi there,
>
> I have been experiencing poor performance with django-admin 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. I have searched extensively for possible
> causes and, after finding nothing and receiving no response on either
> django-users ('list_editable duplicate queries') or IRC, I am starting
> to think that it is a legitimate bug.
While this is worth to cache, you need to index the cache using a
serialized query, not the model.
It is possible to have a different set of choices for each model
instance (for example applying extra filter using another field's
value).
--
Patryk Zawadzki
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Re: contrib.admin:list_editable - ForeignKey Performance is O(m*n)?
Oh, yah, sure. Sorry.
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 FK widgets here requires n*m=25*1=25 database queries:
Form: SELECT "hosts_host"."id", "hosts_host"."name" FROM "hosts_host"
ORDER BY "hosts_host"."name" ASC
Total time: 330 ms
Numer of queries: 25
Twenty five queries is, of course, not a big deal. However, the
default changelist is n=100, and with m=4 this becomes a real problem.
If you comment out the list_editable line or use the fix below
( formfield_overrides = {models.ForeignKey:{'widget':
CachedSelect()}} ), the number of queries returns to O(1).
The jist of what I am wondering is if the changelist is going to allow
editable ForeignKeys, should it be caching the choices rather than
hitting the database every time?
On Jun 29, 7:14 pm, Jeremy Dunck wrote:
> On Wed, Jun 30, 2010 at 2:04 AM,chadc wrote:
>
> ...
>
> > 3. Overriding the ForeignKey widget with a custom CachedSelect widget.
>
> ...
>
> > PS: For the sake of posterity, I have included the code for my
> > CachedSelect widget. Yes, I am aware that using regular expressions to
> > parse the key is a nasty hack. If you have any better ideas, please
> > let me know!
>
> For clarity of what's going on here, would you mind posting an example model?
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Re: contrib.admin:list_editable - ForeignKey Performance is O(m*n)?
On Thu, Jul 1, 2010 at 12:40 AM, chadc wrote: ... > The jist of what I am wondering is if the changelist is going to allow > editable ForeignKeys, should it be caching the choices rather than > hitting the database every time? Yep, your models and explanation are clear. I'm not sure that CachedSelect is a good solution; it seems like there's a general problem with repeated queries within ModelFormSet, not just admin-- it's just cropping up here. I'll try to look at it by tomorrow. File a ticket and let me know the number? -- You received this message because you are subscribed to the Google Groups "Django developers" group. To post to this group, send email to django-develop...@googlegroups.com. To unsubscribe from this group, send email to django-developers+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-developers?hl=en.
Re: contrib.admin:list_editable - ForeignKey Performance is O(m*n)?
Alright. I filed it as #13871 under contrib.admin because I do not understand the larger issue, but please update it as you see fit. Thanks, Jeremy. Ticket Link: http://code.djangoproject.com/ticket/13871 -- You received this message because you are subscribed to the Google Groups "Django developers" group. To post to this group, send email to django-develop...@googlegroups.com. To unsubscribe from this group, send email to django-developers+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-developers?hl=en.
