Hi Xof,
I realized what you meant regd the optimizer and understood why my query
was doing a full table scan. The issue was that column through which I
prefetching has a lot of NULLs so we have a partial index on NOT NULL and
the optimizer is getting fooled by that. Adding a IS NOT NULL in the sam
There's two open tickets to work around this issue.
https://code.djangoproject.com/ticket/25464 which allows passing queryset
override to be used for retrieval and another one that I can't currently
find that allows specifying that a subquery should be used instead of a an
IN clause.
Simon
L
well, prefetch explicitly does joining in python, as in the docs
https://docs.djangoproject.com/en/2.0/ref/models/querysets/#django.db.models.query.QuerySet.prefetch_related
prefetch_related, on the other hand, does a separate lookup for each
relationship, and does the ‘joining’ in Python.
sinc
Hi Xof,
The issue is that, when you do a naive Prefetch you are left with nothing
but Django’s auto generated IN query. I was asking about he recommended way
to make this into a JOIN, which is not obvious how to do with Django
Also in my case the naive IN query on the PK *did not* generate a Inde
> On Jul 25, 2018, at 02:59, Jason wrote:
>
> Where do you get that in the pg documentation? I can't find that anywhere
> (google-fu may be failing me), and we do have some queries with more than 100
> values using IN.
It's slightly more complicated than that. Above 100 entries, the Postgre
Where do you get that in the pg documentation? I can't find that anywhere
(google-fu may be failing me), and we do have some queries with more than
100 values using IN.
On Tuesday, July 24, 2018 at 11:00:48 PM UTC-4, Ram Jayaraman wrote:
>
> Is there a prescribed pattern to optimize Prefetches w
Is there a prescribed pattern to optimize Prefetches when the expected
Prefetch list is known to exceed 100 ? We are on Django 1.8 + Postgres 10.
PG has a limit of 100 for values in IN queries after which the Index on the
said column is not used. For ex: a typical Prefetch generating an IN query
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