Fixed #14231 -- Added an index to the expire_date column on the Sessi…

…on model. Thanks to joeri for the report, via Frodo from Medid.

This won't affect any existing session tables; see the release notes for migration instructions.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14378 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/sessions/models.py

@@ -45,7 +45,7 @@ class Session(models.Model):
     session_key = models.CharField(_('session key'), max_length=40,
                                    primary_key=True)
     session_data = models.TextField(_('session data'))
-    expire_date = models.DateTimeField(_('expire date'))
+    expire_date = models.DateTimeField(_('expire date'), db_index=True)
     objects = SessionManager()
 
     class Meta:

docs/releases/1.3.txt

@@ -165,6 +165,24 @@ To return to the previous rendering (without the ability to clear the
             model = Document
             widgets = {'document': forms.FileInput}
 
+New index on database session table
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Prior to Django 1.3, the database table used by the database backend
+for the :doc:`sessions </topics/http/sessions>` app had no index on
+the ``expire_date`` column. As a result, date-based queries on the
+session table -- such as the query that is needed to purge old
+sessions -- would be very slow if there were lots of sessions.
+
+If you have an existing project that is using the database session
+backend, you don't have to do anything to accommodate this change.
+However, you may get a significant performance boost if you manually
+add the new index to the session table. The SQL that will add the
+index can be found by running the :djadmin:`sqlindexes` admin
+command::
+
+    python manage.py sqlindexes sessions
+
 .. _deprecated-features-1.3:
 
 Features deprecated in 1.3