Sadly I have to admit that I'm not involved with day to day development of
our app anymore (I miss it tremendously). Yesterday I felt nostalgic and
reviewed a few already-merged PRs, just "for fun" we could say. Great was
my surprise when I noticed that one of those PRs was merged with an
`order_by('?')`. We're (and we've always been) using Postgres, and I knew
already that `ORDER BY RANDOM()` is very slow. I just submitted a comment
and it's already been fixed, so it wasn't a big deal. But this got me
thinking:
TLDR;
Some less-experienced developers might not know the issues with
`order_by('?')` (at least with Postgres, the only engine I'm familiar
enough) and it's worth raising a warning. I don't know what's the state of
other engines, it's maybe even worth raising the issue for ANY engine.
It could help newcomers catch these issues early. The docs clearly state it
<https://docs.djangoproject.com/en/3.0/ref/models/querysets/#django.db.models.query.QuerySet.order_by>,
but not everybody reads the docs with such level of detail:
Note: order_by('?') queries may be expensive and slow, depending on the
> database backend you’re using
PS: Sorry for the personal touch of this message, but I think it's worth
the explanation.
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