Now, the UTF8 migration doesn't rely one indexes specified in the .xml files. Instead,

for each table, it fetches all the existing indexes from db, drop them all and, after
utf-8 conversion, rebuilds them.

With this, all the indexes will be exactly the same than the original present in DB, no matter
of their names nor anything else.

So, starting now, to provide a sucessful UTF8 migration we only have to keep updated the
fields .xml info. Bye, bye indexes info.

admin/utfdbmigrate.php

@@ -6,6 +6,8 @@
     require_once($CFG->libdir.'/adminlib.php');
     require_once($CFG->libdir.'/environmentlib.php');
     require_once($CFG->dirroot.'/course/lib.php');
+    require_once($CFG->libdir.'/ddllib.php');      //We are going to need DDL services here
+    require_once($CFG->dirroot.'/backup/lib.php');  //We are going to need BACKUP services here
     require_login();
 
     // decalre once
@@ -220,8 +222,6 @@ function db_migrate2utf8(){   //Eloy: Perhaps some type of limit parameter here
     global $db, $CFG, $dbtablename, $fieldname, $record, $processedrecords;
     $debug = ($CFG->debug > 7);
 
-     //echo date("H:i:s");
-    
     ignore_user_abort(false); // see bug report 5352. This should kill this thread as soon as user aborts.
     
     @set_time_limit(0);
@@ -372,6 +372,31 @@ function db_migrate2utf8(){   //Eloy: Perhaps some type of limit parameter here
                 print_heading("<br><b>Processsing db table ".$dbtablename.'...</b>');
             }
 
+        /*  Insted of relying in the indexes defined for the table in utfmigrate.xml
+            files, we are going to use the MetaIndexes() DB call in order to detect
+            all the table indexes. Once fetched, they are saved in backup tables for
+            safe storage and they are dropped from the table.
+            At the end of the table, we'll fetch them from backup tables and all them
+            will be recreated again.
+            This will ensure that no index in lost in the UTF8 migration process and
+            they will be exactly the same for each server (custom indexes...)
+            Also this will leave free to keep the utfmigrate.xml files in sync for
+            all the existing indexes and we only have to maintain fields in such
+            files
+        */
+
+        /// Calculate all the indexes of the table
+            if ($CFG->dbtype == 'mysql' && $allindexes = $db->MetaIndexes($prefix.$dbtablename)) {
+            /// Send them to backup_ids table for temporal storage if crash
+                backup_putid(9876543210, $prefix.$dbtablename, 1, 1, $allindexes);
+            /// Drop all the indexes
+                $sqlarr = array();
+                foreach ($allindexes as $onekey => $oneindex) {
+                    $sqlarr[] = 'ALTER TABLE '.$prefix.$dbtablename.' DROP INDEX '.$onekey;
+                }
+                execute_sql_arr($sqlarr, true, $debug);
+            }
+
             /**********************************************************
              * This is the by pass structure. It allows us to process *
              * tables on row basis instead of column/field basis      *
@@ -438,7 +463,12 @@ function db_migrate2utf8(){   //Eloy: Perhaps some type of limit parameter here
 
                         if ($CFG->dbtype == 'mysql') {
 
-                            /* Drop the index, because with index on, you can't change it to longblob */
+                            /* Drop the index, because with index on, you can't change it to longblob
+                            
+                               NOTE: We aren't going to drop individual indexes anymore, because we have
+                                     dropped them at the begining of the table iteration, saving them to
+                                     backup temp tables. At the end of the table iteration we are going
+                                     to rebuild them back
 
                             if ($dropindex){    //drop index if index is varchar, text etc type
                                 $SQL = 'ALTER TABLE '.$prefix.$dbtablename.' DROP INDEX '.$dropindex.';';
@@ -446,13 +476,15 @@ function db_migrate2utf8(){   //Eloy: Perhaps some type of limit parameter here
                                 if ($debug) {
                                     $db->debug=999;
                                 }
+
                                 execute_sql($SQL, false); // see bug 5205
                                 execute_sql($SQL1, false); // see bug 5205
 
                                 if ($debug) {
                                     $db->debug=0;
                                 }
-                            } else if ($dropprimary) {    // drop primary key
+                            } else */
+                            if ($dropprimary) {    // drop primary key
                                 $SQL = 'ALTER TABLE '.$prefix.$dbtablename.' DROP PRIMARY KEY;';
                                 if ($debug) {
                                     $db->debug=999;
@@ -715,7 +747,12 @@ function db_migrate2utf8(){   //Eloy: Perhaps some type of limit parameter here
                     $alter = 0;
 
                     if ($CFG->dbtype=='mysql'){
+
                         $SQL = 'ALTER TABLE '.$prefix.$dbtablename;
+                    /*
+                        NOTE: We aren't going to create the indexes back here any more because they
+                              are going to be recreated at the end of the table iteration with
+                              the info saved at the begining of it.
 
                         if (!empty($addindexarray)) {
                             foreach ($addindexarray as $aidx){
@@ -730,6 +767,7 @@ function db_migrate2utf8(){   //Eloy: Perhaps some type of limit parameter here
                                 $alter++;
                             }
                         }
+                    */
 
                         if (!empty($addprimaryarray)) {
                             foreach ($addprimaryarray as $apm){
@@ -775,11 +813,28 @@ function db_migrate2utf8(){   //Eloy: Perhaps some type of limit parameter here
                 if ($debug) {
                     $db->debug=0;
                 }
+
             } else {
 
                 ///posgresql code here
                 ///No we don't need to do anything here
             }
+
+        /// Recreate all the indexes previously dropped and sent to backup
+        /// tables. Retrieve information from backup tables
+            if ($backupindexes = backup_getid(9876543210, $prefix.$dbtablename, 1)) {
+            /// Confirm we have indexes
+                if ($allindexes = $backupindexes->info) {
+                /// Recreate all the indexes
+                    $sqlarr = array();
+                    foreach ($allindexes as $onekey => $oneindex) {
+                        $unique = $oneindex['unique']? 'UNIQUE ' : '';
+                        $sqlarr[] = 'ALTER TABLE '.$prefix.$dbtablename.' ADD '.$unique.'INDEX '.$onekey.
+                                    ' ('.implode(', ', $oneindex['columns']).')';
+                    }
+                    execute_sql_arr($sqlarr, true, $debug);
+                }
+            }
         }
     }
 
@@ -799,14 +854,17 @@ function db_migrate2utf8(){   //Eloy: Perhaps some type of limit parameter here
     
     //These have to go!
     if ($debug) {
-        $db->debug=999;
+        $db->debug=true;
     }
+
     if ($CFG->dbtype == 'postgres7') {
         $backup_db = $GLOBALS['db'];
         $GLOBALS['db'] = &get_postgres_db();
     }
+
     execute_sql('TRUNCATE TABLE '.$CFG->prefix.'cache_text', $debug);
     execute_sql('TRUNCATE TABLE '.$CFG->prefix.'cache_filters', $debug);
+
     if ($CFG->dbtype == 'postgres7') {
         $GLOBALS['db'] = $backup_db;
         unset($backup_db);
@@ -814,6 +872,7 @@ function db_migrate2utf8(){   //Eloy: Perhaps some type of limit parameter here
     if ($debug) {
         $db->debug=0;
     }
+
     //update site language
     $sitelanguage = get_record('config','name', 'lang');
     if (strstr($sitelanguage->value, 'utf8')===false and $sitelanguage->value) {