Merge branch '37145-28' of git://github.com/samhemelryk/moodle

cache/README.md

@@ -266,3 +266,7 @@ There are a couple of considerations to using this method:
 * If you have configured your cache before setting $CFG->altcacheconfigpath you will need to copy it from moodledata/muc/config.php to the destination you specified.
 * This allows you to share a cache config between sites.
 * It also allows you to use unit tests to test your sites cache config.
+
+Please be aware that if you are using Memcache or Memcached it is recommended to use dedicated Memcached servers.
+When caches get purged the memcached servers you have configured get purged, any data stored within them whether it belongs to Moodle or not will be removed.
+If you are using Memcached for sessions as well as caching/testing and caches get purged your sessions will be removed prematurely and users will be need to start again.

config-dist.php

@@ -248,6 +248,11 @@
 //         less reliable. Use memcached where possible or if you encounter
 //         session problems. **
 //
+// Please be aware that when selecting either Memcached or Memcache for sessions that it is advised to use a dedicated
+// memcache server. The memcache and memcached extensions do not provide isolated environments for individual uses.
+// Using the same server for other purposes (MUC for example) can lead to sessions being prematurely removed should
+// the other uses of the server purge the cache.
+//
 // Following setting allows you to alter how frequently is timemodified updated in sessions table.
 //      $CFG->session_update_timemodified_frequency = 20; // In seconds.
 //