生产环境中的PDF导出速度极慢

Question

I use wkhtmltopdf (knp_snappy) to do PDF exports on symfony 3.4. In 'dev' environment everything goes perfectly. In the environment of 'prod' it is another thing, the fast exports are going very well but the voluminous exports are extremely slow.

A large export in 'dev' mode is done in 3 minutes, but is still not finished after 30 minutes in 'prod' mode.

I tried to edit php.ini

opcache.memory_consumption=256

opcache.max_accelerated_files=20000

opcache.validate_timestamps=0

realpath_cache_size=4096K

realpath_cache_ttl=600

I tried several values, but nothing helps.

The part of my code that is slow is this :

$this->get('knp_snappy.pdf')->generateFromHtml($html, 
        $cachePath.$fileNameCreate,
        array( 'header-html'=>$header,
            'footer-html'=>$footer,
            'disable-javascript' => true,
            ));

I did some extra tests, everything works perfectly in dev mode and prod if debug is true. But in prod mode and debug to false it becomes extremely slow again.

Has anyone ever encountered this type of problem?

Do you have any idea of what might cause this?