FYI Django-MySQL supplies an approx_count() method:
https://django-mysql.readthedocs.io/en/latest/queryset_extensions.html#django_mysql.models.approx_count
. It only works on QuerySets without filters. From what I understand it's
possible to get an estimate for filtered queries in MySQL in *some*
circumstances, but you need to be filtering on only one index and not
involve any joins.

I'm in favour of adding this (by whatever name) to core.

On 8 August 2017 at 23:12, Shai Berger <s...@platonix.com> wrote:

> On Wednesday 09 August 2017 00:40:30 Josh Smeaton wrote:
> > We use the explain analyze method at work, but I don't think it's an
> > appropriate thing to include in core.
> >
>
> Agreed.
>
> > I'm not so sure about providing count estimates in core, but I don't
> fully
> > grok how the `estimate_above` would work in practise. Would that execute
> > two queries if the estimate returned a value below the threshold?
>
> That's what I had in mind. But two queries do not have to mean two database
> roundtrips: Since the estimation queries are backend-specific anyway, we
> might
> as well implement `table_count(estimate_above)` using blocks of procedural
> SQL.
>
> I am, again, not suggesting a change to count() at the ORM level -- this
> should be a new API; I *am* suggesting that the admin would use this new
> API
> where appropriate (when the admin queryset has no filters or joins which
> could
> affect the count).
>
> > I think
> > this could be tackled in a separate patch because it would then feed into
> > the expansion of the paginator.
> >
>
> Yes, the idea of controlling whether any count is done, while not entirely
> orthogonal, is certainly of value regardless of this idea, and can (and
> should) be dealt with separately.
>
> Shai.
>



-- 
Adam

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