diff --git a/documentation/optimization.html b/documentation/optimization.html
index 6cb09dba92..b9cfbc9a77 100755
--- a/documentation/optimization.html
+++ b/documentation/optimization.html
@@ -342,7 +342,7 @@ ALTER TABLE user_rel_tag ADD INDEX idx_user_rel_tag_user (user_id);
 In Chamilo 1.10.0 (the first version of the serie), many indexes were forgotten, so you can boost your database by adding the following indexes:<br />
 <pre>
 alter table extra_field_values add index idx_extra_field_values (field_id, item_id);
-alter table usergroup_rel_user add index idx_usergroup_ru (group_id);
+alter table usergroup_rel_user add index idx_usergroup_ru (usergroup_id);
 alter table usergroup_rel_user add index idx_usergroup_ru_u (user_id);
 alter table c_student_publication add index idxstudpub_cid (c_id);
 alter table c_student_publication add index idxstudpub_uid (user_id);
@@ -558,23 +558,23 @@ This is easy, doesn't require a server reload and you should see the results pre
     you should avoid using this technique.
 </p>
 <p>
-You can also mitigate the risk by disabling permissions check only 
+You can also mitigate the risk by disabling permissions check only
 for some static resource like css,js and fonts files.
 <br/>
-For that is required to load header module  
+For that is required to load header module
 in apache (check with a2enmod in your favorite root terminal)<br />
 add theses line after RewriteBase /courses/:
 <pre>
 &lt;IfModule mod_headers.c&gt;
     # all file name ended with these  extensions names will bypass the permission check   (and also served by the browser cache at  the next request)
     &lt;FilesMatch &quot;\.(gif|jpg|jpeg|png|js|pdf|ico|icon|css|swf|avi|mp3|ogg|wav|ttf|otf|eot|woff)$&quot;&gt;
-        Header unset Cache-Control  
-        Header set Cache-Control &quot;public, max-age=29030400&quot; 
-        RequestHeader unset Cookie      
+        Header unset Cache-Control
+        Header set Cache-Control &quot;public, max-age=29030400&quot;
+        RequestHeader unset Cookie
         Header unset ETag
     &lt;/FilesMatch&gt;
 &lt;/IfModule&gt;
-# also adjust files here 
+# also adjust files here
 RewriteRule (\.(html|gif|jpg|jpeg|png|js|pdf|ico|icon|css|swf|avi|mp3|ogg|wav|ttf|otf|eot|woff))$ - [L]
 </pre>
 </p>