MDL-59561 database: Update to creating new indexes in mysql.

When updating the mysql system to utf8mb4 not all tables are
converted to the row format of compressed or dynamic. If a new
index is created there is a possibility that the table could be
using compact or redundant and then an error will be shown saying
that the index size is too large. This fix handles this exception
and converts the table over to compressed.

lib/ddl/database_manager.php

@@ -823,7 +823,20 @@ class database_manager {
             throw new ddl_exception('ddlunknownerror', null, 'add_index sql not generated');
         }
 
-        $this->execute_sql_arr($sqlarr, array($xmldb_table->getName()));
+        try {
+            $this->execute_sql_arr($sqlarr, array($xmldb_table->getName()));
+        } catch (ddl_change_structure_exception $e) {
+            // There could be a problem with the index length related to the row format of the table.
+            // If we are using utf8mb4 and the row format is 'compact' or 'redundant' then we need to change it over to
+            // 'compressed' or 'dynamic'.
+            if (method_exists($this->mdb, 'convert_table_row_format')) {
+                $this->mdb->convert_table_row_format($xmldb_table->getName());
+                $this->execute_sql_arr($sqlarr, array($xmldb_table->getName()));
+            } else {
+                // It's some other problem that we are currently not handling.
+                throw $e;
+            }
+        }
     }
 
     /**

lib/dml/mysqli_native_moodle_database.php

@@ -1917,4 +1917,18 @@ class mysqli_native_moodle_database extends moodle_database {
 
         return true;
     }
+
+    /**
+     * Converts a table to either 'Compressed' or 'Dynamic' row format.
+     *
+     * @param string $tablename Name of the table to convert to the new row format.
+     */
+    public function convert_table_row_format($tablename) {
+        $currentrowformat = $this->get_row_format($tablename);
+        if ($currentrowformat == 'Compact' || $currentrowformat == 'Redundant') {
+            $rowformat = ($this->is_compressed_row_format_supported(false)) ? "ROW_FORMAT=Compressed" : "ROW_FORMAT=Dynamic";
+            $prefix = $this->get_prefix();
+            $this->change_database_structure("ALTER TABLE {$prefix}$tablename $rowformat");
+        }
+    }
 }