Php APC uptime problem

Some notes about APC and the different modes:

• APC's cache is essentially per-process.
• If you use CGI, the process is created, APC creates its cache, and then the process ends and the cache clears. (from what I can find, suPHP seems to be CGI-like).
• If you use FastCGI, Apache spawns one process for each simultaneous request. It keeps them around in case they'll be used again. Each process has its own APC cache.
• If you use the mod_php handler, it shares the cache among all the apache processes, but doesn't run it as the user.

Observations:

• The cache is not resetting on every page refresh, I am seeing several that are being reused that are now five minutes old. Any reconfiguring of the server would've reset this.
• The only way to know you get the same FastCGI process is to be the only client.
• There may be so many requests on your website, that there are several FastCGI processes in use.

Things that should be true:

• While in CGI or SUPHP mode, the values never go up.
• While in fcgid mode, the values go up and down.
• While in mod_php/DSO mode, the values are correct.

Things I'd check (not in any particular order):

• Watch PHP processes under your user (using top or similar). See how long they typically run and if they exit.
• Check Log files to see how many requests is hitting PHP.
• Create a script to check the process ID that the script is run as, if you like write them to a database/file so you can keep track of them easily. Keep loading this page to gather information about how long the process runs.
• Check FastCGI configuration, I'm not sure how cPanel configures it by default because it always had a few issues with some websites when I tried it. There are several options that control how long a process should stay alive. PHP, by default, will exit after 500 requests in FastCGI mode. This is purposeful as some have reported PHP leaking memory after running for a very long time. If your site gets a lot of hits, you may want to bump this number up.

Sounds almost definitely like a peripheral issue influencing what is going on and fairly typical of running Magento in a constrained and contended environment like a VPS.

If your configuration was previously working well and you haven't changed any code or installed any extensions - then it will be an external influence, most likely an increase in traffic - but with a VPS, it is more than likely increased I/O activity.

It sounds exactly like I/O wait - simply installing a graphing tool like Munin would conclusively prove this (showing a correlating in MySQL slow queries with I/O activity/wait).

I'll refer to a few other posts on the same vain - as running Magento in a VPS always yields similar behaviour.

1. https://serverfault.com/a/368649/113375
2. https://serverfault.com/a/367861/113375
3. https://stackoverflow.com/a/8216096