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| author | e0ne <e0ne@e0ne.info> | 2013-09-08 22:57:36 +0300 |
|---|---|---|
| committer | Tim Graham <timograham@gmail.com> | 2013-09-09 09:49:15 -0400 |
| commit | 276e053803c847ce645b1859a162a997a4ee3789 (patch) | |
| tree | 40b6fc0e728a91dd45332bb02cb1d18cd52c3abe | |
| parent | e4274e3da1160997bc78c09ca8f634e04d7438d2 (diff) | |
| download | django-276e053803c847ce645b1859a162a997a4ee3789.tar.gz | |
[1.6.x] Fixed #16895 -- Warned about cost of QuerySet ordering
Thanks outofculture at gmail.com for the suggestion.
Backport of cbf08c6b0c from master
| -rw-r--r-- | docs/ref/models/options.txt | 6 | ||||
| -rw-r--r-- | docs/ref/models/querysets.txt | 6 | ||||
| -rw-r--r-- | docs/topics/db/optimization.txt | 11 |
3 files changed, 23 insertions, 0 deletions
diff --git a/docs/ref/models/options.txt b/docs/ref/models/options.txt index 6413050cb7..36b3cded1f 100644 --- a/docs/ref/models/options.txt +++ b/docs/ref/models/options.txt @@ -216,6 +216,12 @@ 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`` --------------- diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt index c5b835f55f..ec89eacfc4 100644 --- a/docs/ref/models/querysets.txt +++ b/docs/ref/models/querysets.txt @@ -336,6 +336,12 @@ 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 ~~~~~~~ diff --git a/docs/topics/db/optimization.txt b/docs/topics/db/optimization.txt index c1459ae247..cca2e6381b 100644 --- a/docs/topics/db/optimization.txt +++ b/docs/topics/db/optimization.txt @@ -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 ============== |