#20880: Split clone() to clone() and pre_next_op()
-------------------------------------+-------------------------------------
Reporter: akaariai | Owner: nobody
Type: | Status: new
Cleanup/optimization | Version: master
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Accepted
Severity: Normal | Needs documentation: 0
Keywords: | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 0 |
Easy pickings: 0 |
-------------------------------------+-------------------------------------
Changes (by akaariai):
* needs_docs: => 0
* needs_better_patch: => 0
* needs_tests: => 0
* stage: Unreviewed => Accepted
Old description:
> QuerySet and Query clone() methods are doing more than just cloning, they
> are also doing set up for next operation, changing the class of the clone
> if requested, and even throwing away some attribute values.
>
> To make the code a bit more readable the clone() the preparation for next
> op should be splitted away to pre_next_op() method. This also allows
> creating inplace querysets that work precisely like full-clone querysets
> (inplace queryset doesn't do cloning at all). This again allows speeding
> up certain internal operations (like model.save() and
> prefetch_related()), and also allows users to optimise heavy-to-create
> querysets by avoiding clone() overhead.
>
> Patch available from
> https://github.com/akaariai/django/tree/splitted_clone. The inplace
> queryset used for Model.save_base() speeds up model.save() by about 20%
> for a simple m = Model.objects.get(); m.save() benchmark. There are other
> places where similar optimisations could be used. Prefetch speedup is
> tracked in ticket #20577.
New description:
QuerySet and Query clone() methods are doing more than just cloning, they
are also doing set up for next operation, changing the class of the clone
if requested, and even throwing away some attribute values.
To make the code a bit more readable the clone() method should be splitted
to clone() part and pre_next_op() part. This also allows creating inplace
querysets that work precisely like full-clone querysets. A queryset is
called inplace if it doesn't do cloning at all between operations. This
again allows speeding up certain internal operations like model.save() and
prefetch_related(), and also allows users to optimise heavy-to-create
querysets by avoiding clone() overhead.
Patch available from
https://github.com/akaariai/django/tree/splitted_clone. The inplace
queryset used for Model.save_base() speeds up model.save() by about 20%
for a simple m = Model.objects.get(); m.save() benchmark. There are other
places where similar optimisations could be used. Prefetch speedup is
tracked in ticket #20577.
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Ticket URL: <https://code.djangoproject.com/ticket/20880#comment:1>
Django <https://code.djangoproject.com/>
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