public function getIndexedDocuments()
    {
        $db = $this->getSearchDbHandle();
        $sql = '
			SELECT count(DISTINCT documentPath) AS indexedDocuments
			  FROM term_frequency
		';
        if (!$stmt = $db->query($sql)) {
            $errorInfo = $db->errorInfo();
            $errorMsg = $errorInfo[2];
            throw new \RuntimeException('SQLite Exception: ' . $errorMsg . ' in SQL: <br /><pre>' . $sql . '</pre>');
        }
        $result = $stmt->fetch(\PDO::FETCH_COLUMN);
        if (false === $result) {
            $errorInfo = $db->errorInfo();
            $errorMsg = $errorInfo[2];
            throw new \RuntimeException('SQLite Exception: ' . $errorMsg . ' in SQL: <br /><pre>' . $sql . '</pre>');
        }
        return (int)$result;
    }