OpenCart 1.4.x/1.5.x compatible!
1. Copy mysql_cached.php file into the /system/library/database
2. Change /config.php file only:
define('DB_DRIVER', 'mysql_cached');
define('DB_CACHED_EXPIRE', 120);
3. For reset SQL cache, you can save in cache with key 'sql_globalresetcache' current time (time()).
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