#25230: Change to Query.get_count() causes big performance hit
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Reporter: dexity | Owner: nobody
Type: | Status: new
Cleanup/optimization |
Component: Database layer | Version: 1.8
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by jarshwah):
akaariai's argument against fixing this makes sense to me.
The distinct in `Model.objects.distinct().count()` is redundant, because
the `pk` enforces that each row will be distinct anyway. For the cases
where `distinct` will actually change the result, then a subquery is
required.
So even if we decide to fix this, I don't think it warrants release
blocker status. Fix the queryset by removing the redundant `distinct`. If
we can demonstrate that changing the queryset to be correct is non-
obvious, then I think that might push the case for implementing a fix.
Really though, distinct is very rarely useful, and is indicative of a
poorly constructed query (in sql or in django). Obviously there are useful
distinct queries, but they are the exception in my experience.
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Ticket URL: <https://code.djangoproject.com/ticket/25230#comment:7>
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