OPcache improves PHP performance by storing precompiled script bytecode in shared memory, thereby removing the need for PHP to load and parse scripts on each request.
Enables the opcode cache. When disabled, code is not optimised or cached. The setting opcache.enable can not be enabled at runtime through ini_set(), it can only be disabled. Trying to enable it at in a script will generate a warning.
By default opcache only uses 128MB on each PHP version you are using. To change you can follow these instructions:opcache is help so much with speed but...
opcache need more ram, please consider this one.