If you have upgraded (or planning an upgrade) your Drupal 7 platform to Ubuntu 14.04 then you most likely know about the “install creates 31 tables then stops” and “Installation failure when opcode cache is enabled” issues. Which is caused by a problem between the Drupal code and OPcache.
A few words about the OPcache. Ubuntu 14.04 comes with php 5.5, which has Zend OPcache built-in. If you have already tried to install APC extension for your php setup, you failed. And if you googled about this failure then you heard that the APC is included in php5.5. Well, you can say that. Actually, the type of these caching solutions are called “OpCode Cache“. “APC” is one of them. “Zend OPcache” is another one; and this Zend OPcache (or OPcache for short) is built into php 5.5, not APC.
The Drupal problem has been fixed for D8 on this issue but no patch is available for D7 yet.
The workaround is to disable the OPcache, which is enabled by default. It is a setting in php.ini file.
The question has been raised if disabling the OPcache before installation and enabling it right after would be good enough. While I don’t have a solid answer for that, it should be good enough to keep it disabled during installation and upgrades. I permanately turned it off on my test site. Maybe I should turn it on again and do some tests..
Another question I have seen but not answered was, if we can disable the OPcache per site basis. Like disabling it for a D7 sites and enabling it for others.
Yes, we can do that. As the title of this article suggests, we can disable OPcache per site basis but we cannot enable it whenever we want it; it should be enabled by default. If you have disabled it through php.ini file, then you need to revert it back.
Placing below line in your “settings.php” file will disable it.
However, I like the “.htaccess” method much better.
php_flag opcache.enable Off
Remember that your apache config should have “AllowOverride All” in order to make the .htaccess method work; which is also a requirement for installing & running Drupal websites.