MPM Worker settings calculation

[rewt rewt <rewt@xxxxxxxxxxxxxxx>]

Hello,

After many performances issues with mpm prefork (high memory) i would like to use the MPM worker wich seems better for high traffic sites.

I have been able to estimate the RAM per httpd process in prefork around 25m.

With the prefork setting i have calculate MaxClients this way:

MaxClients = ((TOTAL_MEMORY - MEMORY_USED_BY_HTTD)/MEDIUM_SIZE_OF_HTTPD_PROCESSES)-10%

It means that for a 8GB RAM server using arround 25M for each connections with a system usage of around 1,5G i will have:

MaxClients=((8000000 - 2000000)/25000)-10%

MaxClients=216 (arround 220)

Correct, right ?

But now i want to use MPM worker (with FastCGI for PHP, APC and mod_mem_cache (if it is possible ?)).

My issue is that i don't know how to calculate the settings for MaxClients, ThreadPerChild, ThreadStackSize etc...

And the documentation even on the Apache site is not explained anywhere (as far as i have seen)

I am using a VPS with 32Gb of RAM and 8 vCPU. (i d like to use haproxy as a reverse proxy with 2 or 3 VPS like that in the backend)

The PHP app is using around 25m (calculated with  with prefork)

What could be the best setting with these value to have the maximum number of request at the same time without issue ?

And so what will be the maximum MaxClients i can set with these value?

Many thanks in advance for your kind help.