[3.0.x] Improved sessions notes in deployment checklist.

- Added note to clear old sessions when using database-backend.
- Made note to consider the cache backend more generic.
Backport of 66b06822d05ca1cf897745e7cb3c89adc53363ba from master

docs/howto/deployment/checklist.txt

@@ -109,9 +109,6 @@ and in production. Django defaults to per-process :ref:`local-memory caching
 Cache servers often have weak authentication. Make sure they only accept
 connections from your application servers.
 
-If you're using Memcached, consider using :ref:`cached sessions
-<cached-sessions-backend>` to improve performance.
-
 :setting:`DATABASES`
 --------------------
 
@@ -187,6 +184,15 @@ Performance optimizations
 Setting :setting:`DEBUG = False <DEBUG>` disables several features that are
 only useful in development. In addition, you can tune the following settings.
 
+Sessions
+--------
+
+Consider using :ref:`cached sessions <cached-sessions-backend>` to improve
+performance.
+
+If using database-backed sessions, regularly :ref:`clear old sessions
+<clearing-the-session-store>` to avoid storing unnecessary data.
+
 :setting:`CONN_MAX_AGE`
 -----------------------
 

docs/topics/http/sessions.txt

@@ -599,6 +599,8 @@ of ``request.session`` as described above in `using sessions in views`_.
     Django applications which have the
     :setting:`SESSION_EXPIRE_AT_BROWSER_CLOSE` setting enabled.
 
+.. _clearing-the-session-store:
+
 Clearing the session store
 ==========================