Optimize Serializer Performance in Django Rest Framework

Question

I'm developing a web app using Django and Django Rest Framework and struggling with slow API responses which appear to be based on fetching data from related tables.

Test case 1 runs very quickly because the fields are directly tied to the Host model. As soon as I introduce a many-to-many field, it slows down dramatically.

Test case 1 - takes 250ms

serializers.py

class HostSerializer(serializers.Serializer):
    created = serializers.DateTimeField()
    last_updated = serializers.DateTimeField()
    name = serializers.CharField();

Test case 2 - takes 30s

serializers.py

class HostSerializer(serializers.Serializer):
    created = serializers.DateTimeField()
    last_updated = serializers.DateTimeField()
    name = serializers.CharField();
    applications = serializers.SerializerMethodField(read_only=True)

    def get_applications(self, instance):
        return [item.name for item in instance.applications.all()]

models.py

class Host(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    last_updated = models.DateTimeField(auto_now=True)
    name = models.CharField(unique=True, max_length=settings.MAX_CHAR_COUNT)
    ip_addresses = models.ManyToManyField(IPAddress, blank=True)
    open_ports = models.ManyToManyField(Port, blank=True)
    domain = models.ForeignKey('Domain', on_delete=models.CASCADE)

    applications = models.ManyToManyField(Application, blank=True)
    tls = models.ForeignKey(TLS, on_delete=models.CASCADE, blank=True, null=True)

    class Meta:
        ordering = ['name']

    def __str__(self):
        return self.name

    def __repr__(self):
        return self.name

    def __eq__(self, other):
        if isinstance(other, Host):
            return self.name == other.name
        return False

    def __hash__(self) -> int:
        return hash(self.name)

    def __lt__(self, other):
        return self.name < other.name

views.py

class HostList(generics.ListAPIView):
    """
    List all hosts for a given domain
    """
    host_service = HostService()
   
    def get(self, request, domain_name, format=None):
        hosts = self.host_service.find_hosts_by_domain_name(domain_name)

        if len(hosts) == 0:
            return Response(status=status.HTTP_404_NOT_FOUND)

        serializer = HostSerializer(hosts, many=True)
        page = self.paginate_queryset(serializer.data)
        return self.get_paginated_response(page)

Could you post HostService .find_hosts_by_domain_name method code? — wiaterb
– wiaterb, Commented Jul 29, 2020 at 13:54

A_B · Accepted Answer · 2020-07-31 03:18:02Z

2

I was able to resolve my performance issues by making a few changes to the view.

Refactored the view and added prefetch_related to views.py

class HostList(generics.ListAPIView):
    """
    List all hosts for a given domain
    """
    host_service = HostService()
    serializer_class = HostSerializer

    def get_queryset(self):
        return Host.objects.filter(domain__name__iexact=self.kwargs['domain_name'])\
            .prefetch_related('applications')

answered Jul 31, 2020 at 3:18

A_B

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