Merge pull request #3324 from patrickbirch/PS-5.7-5427

PS-5427 Document the correct distribution upgrade process for Percona…

doc/source/upgrading_guide_56_57.rst

@@ -337,3 +337,18 @@ After this is done, just restart the server as usual:
 .. code-block:: bash
 
   $ service mysql restart
+
+Performing a Distribution upgrade in-place on a System with installed Percona packages
+--------------------------------------------------------------------------------------------
+
+The recommended process for performing a distribution upgrade on a system with
+the Percona packages installed is the following:
+
+    1. Record the installed Percona packages
+    2. Backup the data and configurations
+    3. Uninstall the Percona packages without removing the configurations or
+       data
+    4. Perform the upgrade by following the distribution upgrade instructions
+    5. Reboot the system
+    6. Install the Percona packages intended for the upgraded version of the
+       distribution