How can I enable opcache preloading in PHP 7.4?

Question

I'd like to enable opcache preloading (RFC) on my production servers in PHP 7.4.

I'm using Symfony 4 if it changes anything.

Sn

Not sure how much reddit.com/r/PHP/comments/e8pgzi/… will affect any plans for using it. – Jovi

Symfony on preloading – Tracheid

Check this article. Also read that bug Nigel posted, as it seems quite critical for the time being. – Piecedyed

Answer 1

According to the blog post this appears to be trivial. Apparently Symfony since 4.4 generates a preload script which has to be set in the php.ini:

opcache.preload=/path/to/project/var/cache/prod/App_KernelProdContainer.preload.php

I did some tests in my local Docker environment and this is how it went:

PHP 7.3 without OPcache (current)

Requests per second:    8.75 [#/sec] (mean)
Time per request:       114.402 [ms] (mean)

PHP 7.4 without OPcache

Requests per second:    11.44 [#/sec] (mean)
Time per request:       87.417 [ms] (mean)

PHP 7.4 with OPcache, without preloading (Apache + modphp)

Requests per second:    30.25 [#/sec] (mean)
Time per request:       33.053 [ms]

PHP 7.4 with OPcache, without preloading (nginx + php fpm)

Requests per second:    40.00 [#/sec] (mean)

Unfortunately I was not able to enable the preloading :( I encountered following errors (in both Apache+Mod and Nginx+FPM):

double free or corruption (!prev)
child pid 17 exit signal Aborted (6), possible coredump (…)

This feature looks like a WIP though. I'm going to revalidate this answer when I'm able to use this preloading thing. In overall I'm quite impressed, +30% performance just by upgrading from PHP 7.3 to 7.4.

Sn

I am trying preload on Symfony with fairly large size application, I am getting errors like Cannot declare class because the name is already in use. I am using require_once in preload file to be able to load dependencies as well which probably is conflicting with loaded classes. – Teage

@Teage i've got the same issue. Did you eventually find the reason ? – Measly

Sure, upgrade PHP to the latest version. – Sn

@emix You might want to update your answer since its really great and I almost obmitted it because of the written conclusion that it does not work. Fortunately I saw your comment in time. – Commerce

One day for sure ;) – Sn

Answer 2

First of all you should add:

opcache.preload=/path/to/project/preload.php

to your php.ini

Then in your PHP script you should pass in opcache_compile_file($file); each file you want to preloaded.

Jolynjolynn