- Patch #838528 by marcingy: primary index on session table is not update when upgrading.

includes/update.inc

@@ -586,6 +586,10 @@ function update_fix_d7_requirements() {
     // Add ssid column and index.
     db_add_field('sessions', 'ssid', array('description' => "Secure session ID. The value is generated by PHP's Session API.", 'type' => 'varchar', 'length' => 128, 'not null' => TRUE, 'default' => ''));
     db_add_index('sessions', 'ssid', array('ssid'));
+    // Drop existing primary key.
+    db_drop_primary_key('sessions');
+    // Add new primary key.
+    db_add_primary_key('sessions', array('sid', 'ssid'));
 
     variable_set('update_d7_requirements', TRUE);
   }