Question Plesk PHP-FPM APCu SHM Mismatch: phpinfo() shows 512M but apcu_sma_info() returns ~32M

[marekp]

Server operating system version

CentOS 7.9

Plesk version and microupdate number

Plesk 18.0.69

Hello Plesk community,
I’m running a CakePHP 4.6 application on CentOS 7.9 with Plesk 18. My PHP version is 8.2.28, and I have PHP-FPM enabled for the domain. In Plesk’s PHP Settings for this domain, I added:

apc.enabled = 1
apc.shm_size = 512M

After applying and letting Plesk restart FPM, I verified via a simple phpinfo() call that apc.shm_size is indeed set to 512M in the FPM environment. However, when I call apcu_sma_info() from a CakePHP controller (i.e. executed via the browser, not CLI), I see:

Array
(
[num_seg] => 1
[seg_size] => 33554312 // ~32 MB in bytes
[avail_mem] => 31328296
[block_lists] => Array(…)
)

Despite ini_get('apc.shm_size') outputting “512M,” the actual segment size in apcu_sma_info() is only ~33,554,312 bytes, indicating FPM has only reserved ~32 MB of APCu shared memory. I need to understand:

1. Where exactly is APCu’s ini for the active PHP-FPM pool?
2. Why does phpinfo() report 512M but apcu_sma_info() still show only ~32M?
3. How can I force the FPM workers to truly initialize APCu with 512M SHM?

I have checked:

• SAPI: Confirmed PHP_SAPI is fpm-fcgi.
• Loaded php.ini: /opt/plesk/php/8.2/etc/php.ini
• Scanned ini files: includes /opt/plesk/php/8.2/etc/php.d/apcu.ini
• ini_get('apc.shm_size'): 512M
• apcu_sma_info()['seg_size']: 33554312

It looks like the FPM-workers may still be using some default (32M) instead of picking up the 512M override. Any pointers on where Plesk keeps the pool-specific APCu configuration, or how to ensure the FPM process actually reserves the full 512M? Thanks in advance!

 

[Sebahat.hadzhi]

Hello, @marekp . APCu is not officially supported by Plesk and was not tested extensively, so I cannot confirm that for sure. Our engineers previously reviewed a similar case and were able to determine (through a test script) that the limit of apc.shm_size for the environment is the manually defined one (e.g. 512MB), and the 32MB memory segment limit is set on the system level.

If it's absolutely necessary, what you can try is adding apc.shm_size = 512M to /opt/plesk/php/8.2/etc/php.d/apcu.ini. However, please proceed with caution and at your own risk.