Cache tracker enabled per table

This can be executed quite a lot of times during import and there is no
reason to query database again during that.

Fixes #13318

Signed-off-by: Michal Čihař <michal@cihar.com>

ChangeLog

@@ -14,6 +14,7 @@ phpMyAdmin - ChangeLog
 - issue #13092 Gracefully handle early fatal errors in AJAX requests
 - issue #13327 Fixed Incorrect NavigationTreeEnableExpansion default value in the documentation
 - issue #13008 Fixed export of database with a lot of tables
+- issue #13318 Improved performance when importing with enabled tracking
 
 4.7.1 (2017-05-25)
 - issue #13132 Always execute tracking queries as controluser

libraries/Tracker.php

@@ -23,6 +23,11 @@ class Tracker
      */
     static protected $enabled = false;
 
+    /**
+     * Cache to avoid quering tracking status multiple times.
+     */
+    static protected $_tracking_cache = array();
+
     /**
      * Actually enables tracking. This needs to be done after all
      * underlaying code is initialized.
@@ -111,6 +116,10 @@ static public function isTracked($dbname, $tablename)
         if (! self::$enabled) {
             return false;
         }
+
+        if (isset(self::$_tracking_cache[$dbname][$tablename])) {
+            return self::$_tracking_cache[$dbname][$tablename];
+        }
         /* We need to avoid attempt to track any queries
          * from PMA_getRelationsParam
          */
@@ -127,9 +136,11 @@ static public function isTracked($dbname, $tablename)
         " AND table_name = '" . $GLOBALS['dbi']->escapeString($tablename) . "' " .
         " ORDER BY version DESC LIMIT 1";
 
-        $result = $GLOBALS['dbi']->fetchValue($sql_query, 0, 0, $GLOBALS['controllink']);
+        $result = $GLOBALS['dbi']->fetchValue($sql_query, 0, 0, $GLOBALS['controllink']) == 1;
+
+        self::$_tracking_cache[$dbname][$tablename] = $result;
 
-        return ($result == 1);
+        return $result;
     }
 
     /**