Fixed #18676 -- Allow fast-path deletion of objects

Objects can be fast-path deleted if there are no signals, and there are
no further cascades. If fast-path is taken, the objects do not need to
be loaded into memory before deletion.

Thanks to Jeremy Dunck, Simon Charette and Alex Gaynor for reviewing
the patch.

2 files changed, 21 insertions, 0 deletions

diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt
index 749a979db6..d17d869164 100644
--- a/docs/ref/models/querysets.txt
+++ b/docs/ref/models/querysets.txt
@@ -1667,6 +1667,21 @@ methods on your models. It does, however, emit the
 :data:`~django.db.models.signals.post_delete` signals for all deleted objects
 (including cascaded deletions).
 
+.. versionadded:: 1.5
+    Allow fast-path deletion of objects
+
+Django needs to fetch objects into memory to send signals and handle cascades.
+However, if there are no cascades and no signals, then Django may take a
+fast-path and delete objects without fetching into memory. For large
+deletes this can result in significantly reduced memory usage. The amount of
+executed queries can be reduced, too.
+
+ForeignKeys which are set to :attr:`~django.db.models.ForeignKey.on_delete`
+DO_NOTHING do not prevent taking the fast-path in deletion.
+
+Note that the queries generated in object deletion is an implementation
+detail subject to change.
+
 .. _field-lookups:
 
 Field lookups
diff --git a/docs/releases/1.5.txt b/docs/releases/1.5.txt
index fddd03d421..5636a2b34b 100644
--- a/docs/releases/1.5.txt
+++ b/docs/releases/1.5.txt
@@ -149,6 +149,12 @@ Django 1.5 also includes several smaller improvements worth noting:
 * Django now provides a mod_wsgi :doc:`auth handler
   </howto/deployment/wsgi/apache-auth>`
 
+* The :meth:`QuerySet.delete() <django.db.models.query.QuerySet.delete>`
+  and :meth:`Model.delete() <django.db.models.Model.delete()>` can now take
+  fast-path in some cases. The fast-path allows for less queries and less
+  objects fetched into memory. See :meth:`QuerySet.delete()
+  <django.db.models.query.QuerySet.delete>` for details.
+
 Backwards incompatible changes in 1.5
 =====================================