OPcache is an opcode cache for PHP. It is bundled with PHP 5.5.0 and later.
The following settings work really well with Drupal. For Ubunti 14.04 , these following file can be modified to incorporate the changes
/etc/php5/apache2/php.iniConfiguration:
opcache.enable=1
opcache.memory_consumption=256
opcache.max_accelerated_files=4000
opcache.revalidate_freq=60
opcache.fast_shutdown=1Definition:
opcache.memory_consumption - The size of the shared memory storage used by OPcache, in megabytes.
opcache.max_accelerated_files - The maximum number of keys (and therefore scripts) in the OPcache hash table.
opcache.revalidate_freq=60 - How often to check script timestamps for updates, in seconds.
opcache.fast_shutdown=1 - The fast shutdown sequence doesn't free each allocated block, but lets the Zend Engine Memory Manager do the work.
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http://getlevelten.com/blog/kyle-taylor/tuning-drupal-performance-digita...
https://www.scalingphpbook.com/best-zend-opcache-settings-tuning-config/