But Why is the (Django) Admin Slow? - PyCon 2019

Slides from my PyCon 2019 talk discussing common Django Admin performance hiccups and ways to debug them using the Django Debug Toolbar.

Video for this presentation can be found here: https://www.youtube.com/watch?v=f8cFjiyxQuQ

Transcript

1. BUT, WHY IS THE ADMIN SLOW? Jacinda Shelly PyCon 2019
2. ABOUT ME • CTO @ Doctor On Demand • Long-time Python and Django user • Love exercise, reading, and family time
3. THANK YOU PYCON! • Childcare at the conference made it easier for me to give this talk
4. SO, YOU JUST STARTED USING THE ADMIN
5. FIRST, YOU FEEL LIKE THIS
7. THEN PEOPLE START USING IT
9. BUT THEN…
11. AND NOW YOU’RE DEALING WITH…
13. SO…
14. A LIBRARY
16. class LibraryUser(AbstractUser): ''' Custom user for our library project. Inherits from AbstractUser, which has the following fields: - username - first_name - last_name - email - is_staff - is_active - date_joined ''' birthdate = models.DateField( 'Date of Birth', null=True, blank=False ) gender = models.CharField( "Gender", max_length=1, choices=GENDER_CHOICES, blank=False ) books = models.ManyToManyField( 'stacks.Book', through=‘stacks.LoanedBook' ) def __str__(self): return self.get_full_name()
17. class Author(models.Model): """ Model representing the author of a work. """ last_name = models.CharField(max_length=32) first_name = models.CharField(max_length=32) def __str__(self): return self.full_name() def full_name(self): return ", “.join( [self.last_name, self.first_name] )
18. class Book(AbstractItem): title = models.CharField(max_length=4000) page_count = models.PositiveIntegerField() daily_fine = models.DecimalField( max_digits=4, decimal_places=2, default="0.25", help_text=_( "Amount the patron will be fined per day" " for an overdue library book." ), ) def __str__(self): return self.title
19. class LoanedBook(models.Model): patron = models.ForeignKey( settings.AUTH_USER_MODEL, on_delete=models.CASCADE ) book = models.ForeignKey(Book, on_delete=models.CASCADE) checkout_date = models.DateField() due_date = models.DateField() return_date = models.DateField(null=True, blank=True) times_renewed = models.IntegerField(default=0) fine_paid = models.NullBooleanField() def __str__(self): return ": ".join([str(self.patron), str(self.book)])
20. https://django-debug-toolbar.readthedocs.io/ INSTALLED_APPS = [ # … 'debug_toolbar' ] INTERNAL_IPS =['127.0.0.1',] MIDDLEWARE_CLASSES = [ # … 'debug_toolbar.middleware.DebugToolbarMiddleware' ]
21. Quick Tip! * INTERNAL_IPS is a whitelist of IPs making requests to your server
24. First, we get all the loaned book entries Then, we get related objects ONE. BY. ONE.
25. The Culprit
26. def __str__(self): return ": ".join([str(self.patron), str(self.book)]) Problem: Solution 1: @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_display = ('patron', 'book') Solution 2a: @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = True Solution 2b: @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = ('patron', 'book')
27. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_display = ('patron', 'book')
28. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = True Now Let’s Try:
29. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = True
30. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = ('patron', ) Be more specific:
31. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = ('patron', )
33. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = (‘patron’, ‘book') Full Solution 2b:
35. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = ('patron', 'book') def get_queryset(self, request): qs = super(LoanedBookAdmin, self).get_queryset(request) qs = qs.only("patron__first_name", "patron__last_name", "book__daily_fine") return qs Well, let’s see…
36. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = ('patron', 'book') def get_queryset(self, request): qs = super(LoanedBookAdmin, self).get_queryset(request) qs = qs.only("patron__first_name", "patron__last_name", "book__daily_fine") return qs
38. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = ('patron', 'book') def get_queryset(self, request): qs = super(LoanedBookAdmin, self).get_queryset(request) qs = qs.only("patron__first_name", "patron__last_name", "book__title") return qs Fixed!
39. @admin.register(LoanedBook) class LoanedBookAdmin(admin.ModelAdmin): list_select_related = ('patron', 'book') def get_queryset(self, request): qs = super(LoanedBookAdmin, self).get_queryset(request) qs = qs.only("patron__first_name", "patron__last_name", "book__title") return qs
40. Now, we want to try something else # models.py class Book(AbstractItem): authors = models.ManyToManyField(Author, related_name=“works") def authors_display(self): return "; ".join([str(author) for author in self.authors.all()]) # admin.py @admin.register(Book) class BookAdmin(admin.ModelAdmin): list_display = ("__str__", "authors_display") list_select_related = True
43. Solution @admin.register(Book) class BookAdmin(admin.ModelAdmin): list_display = ("__str__", "authors_display") def get_queryset(self, request): qs = super(BookAdmin, self).get_queryset(request) qs = qs.prefetch_related("authors") return qs
46. Next Up - Counting! # models.py class Author(models.Model): # ... def book_count(self): return self.works.count() # admin.py @admin.register(Author) class AuthorAdmin(admin.ModelAdmin): fields = ("first_name", "last_name") list_display = ("__str__", "book_count")
48. Custom Querysets to the Rescue (again)! from django.db.models import Count @admin.register(Author) class AuthorAdmin(admin.ModelAdmin): fields = ("first_name", "last_name") list_display = ("__str__", "book_count") def get_queryset(self, request): qs = super(AuthorAdmin, self).get_queryset(request) qs = qs.annotate( book_count=Count("works") ) return qs
51. A FEW OTHER TIPS Decrease ModelAdmin.list_per_page Set ModelAdmin.show_full_result_count to False Use a custom Paginator Sorting can be expensive
52. THANK YOU https://github.com/jacinda/ pycon2019-admin-talk @jacindashelly Doctor On Demand is hiring!