memory_limit problem in opencart or anyother website

error:-

Fatal error: Allowed memory size of 138412032 bytes exhausted (tried to allocate 71 bytes) in /home/xxxxxxx/public_html/xxxxxxxxxxxx/vqmod/vqcache/vq2-system_engine_controller.php on line 79


simple solution:-

<?php ini_set('memory_limit', '-1'); ?>

write this code on config.php in first line.its unlimited.