query optimisations for notifications - use a specific index only

include/dba/dba_driver.php

@@ -321,6 +321,10 @@ function db_concat($fld, $sep) {
 	return \DBA::$dba->concat($fld, $sep);
 }
 
+function db_use_index($str) {
+	return \DBA::$dba->use_index($str);
+}
+
 /**
  * @brief Execute a SQL query with printf style args.
  *

include/dba/dba_pdo.php

@@ -111,6 +111,15 @@ class dba_pdo extends dba_driver {
 		}
 	}
 
+	function use_index($str) {
+		if($this->driver_dbtype === 'pgsql') {
+			return '';
+		}
+		else {
+			return 'USE INDEX( ' . $str . ')';
+		}
+	}
+
 	function quote_interval($txt) {
 		if($this->driver_dbtype === 'pgsql') {
 			return "'$txt'";