PHP 5.6: What does “opcache: interned string buffers overflow” mean?

Question

I am running PHP 5.6 and enabled the compiled-in module opcache. Now when I read the warnings inside my error log, I get these messages every few milliseconds:

Warning Interned String buffer overflow

There is no description to this error using this google search. However, the source code says, there may not be enough memory? Did I read this correctly?

So, to my understanding it is absolutely okay if cache gets exhausted and will be reused/recycled for new strings. If not, what am I missing?

I set opcache.interned_string_buffer from 4 to 8 MiB, but no luck yet.

Answer 1

opcache.interned_strings_buffer - A pretty neat setting with like 0 documentation. PHP uses a technique called string interning to improve performance— so, for example, if you have the string "foobar" 1000 times in your code, internally PHP will store 1 immutable variable for this string and just use a pointer to it for the other 999 times you use it. Cool. This setting takes it to the next level— instead of having a pool of these immutable string for each SINGLE php-fpm process, this setting shares it across ALL of your php-fpm processes. It saves memory and improves performance, especially in big applications.

https://www.scalingphpbook.com/best-zend-opcache-settings-tuning-config/

Answer 2

There is an ongoing bug that affects some users when opcache.interned_string_buffer is not set high enough. The bug causes Apache to crash so you would definitely know if you were experiencing the issue.

I recommend temporarily creating a php file such as info.php and adding

<?php phpinfo(); ?>

view the file in your browser to easily see "Interned Strings Used memory" and make sure you have some free memory. I have a fairly large wordpress site and I have my memory limit set at 32. I consistently have about 14mb interned strings memory used.