Commit cbf08c6b authored by e0ne's avatar e0ne Committed by Tim Graham
Browse files

Fixed #16895 -- Warned about cost of QuerySet ordering 

Thanks outofculture at gmail.com for the suggestion.
parent 1185370c

docs/ref/models/options.txt

+6 −0
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@@ -221,6 +221,12 @@ Django quotes column and table names behind the scenes. 


        ordering = ['-pub_date', 'author']



.. warning::



    Ordering is not a free operation. Each field you add to the ordering

    incurs a cost to your database. Each foreign key you add will

    impliclty include all of its default orderings as well.



``permissions``

---------------

docs/ref/models/querysets.txt

+6 −0
Original line number Diff line number Diff line
@@ -334,6 +334,12 @@ You can tell if a query is ordered or not by checking the 
:attr:`.QuerySet.ordered` attribute, which will be ``True`` if the

``QuerySet`` has been ordered in any way.



.. warning::



    Ordering is not a free operation. Each field you add to the ordering

    incurs a cost to your database. Each foreign key you add will

    impliclty include all of its default orderings as well.



reverse

~~~~~~~

docs/topics/db/optimization.txt

+11 −0
Original line number Diff line number Diff line
@@ -306,6 +306,17 @@ instead of:: 


   entry.blog.id



Don't order results if you don't care

-------------------------------------



Ordering is not free; each field to order by is an operation the database must

perform. If a model has a default ordering (:attr:`Meta.ordering

<django.db.models.Options.ordering>`) and you don't need it, remove

it on a ``QuerySet`` by calling

:meth:`~django.db.models.query.QuerySet.order_by()` with no parameters.



Adding an index to your database may help to improve ordering performance.



Insert in bulk

==============