I'm using django's (1.8.5) conditional annotation in order to add filtered
data to each object dynamically. But the issue is that it's very slow on
all machines I've tested it.
What it does is basically adds data to each user. How many messages they
sent from provided date, how many messages have failed and how many
messages they sent from yesterday. There is not much data. Just about 100
users and each of them may have about 50 messages daily.
objects = self.get_queryset().annotate(sent_count=
Sum(
Case(When(messages__date_sent__gte=date_from, then=1)),
output_field=IntegerField()
),
error_count=
Sum(
Case(When(messages__status__iexact='error', then=1)),
output_field=IntegerField()
),
sent_yesterday=
Sum(
Case(When(messages__date_sent__gte=yesterday, then=1)),
output_field=IntegerField()
)
)
When checking a query, it takes up to 15 seconds to execute it. Am I doing
something wrong or is conditional annotation not designed for things like
this?
After looking at the generated query, it seems that Django is trying to
GROUP BY by every available field in both models and their related models..
After adding prefetch_related to some related models, issue was fixed on
one machine, but still persists on the second one.
Is this a bug?
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