Hello,
We have a lot of these type of thing throughout our code:
class PropertyViewSet(V2Mixin, V2BulkUpdateViewSet):
queryset = (
Property.objects.all()
.prefetch_related(
'servicecontract_set',
'servicecontract_set__service',
'client__primary_contact',
'client__tags',
'tags',
)
.annotate(inspectionitem_count=Count('inspectionitem'))
)
The .annotate was fine when our dataset was small, but now it's become a
real performance issue. It adds about 500ms to the query time and
surprisingly 4seconds to the page load time, I suspect due to the ORM doing
so much busywork on the data that comes via the join.
Does anyone have an idea for doing fast annotations of only the current
page of data? e.g. it's trivial to issue a separate (and fast) query
against the InspectionItem table grouping by the Property to give us the
counts for e.g. the 100 results to be displayed on the current page. I was
thinking some sort of SerializerMethodField which primed a cache on first
hit.
Has anyone done anything like this?
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