Apache MaxRequestWorkers issue not resolving

Question

My website generate when I tried to hit 1000 requests per second on it. I am seeing the following errors in my apache logs

Apr 06 00:00:33 ns503772******100.net httpd[9585]: AH00515: WARNING: MaxRequestWorkers of 2000 would require 80 servers and
Apr 06 00:00:33 ns503772******100.net httpd[9585]: would exceed ServerLimit of 16, decreasing to 400.
Apr 06 00:00:33 ns503772******100.net httpd[9585]: To increase, please see the ServerLimit directive.

My current setting was following

<IfModule mpm_event_module>
LoadModule cgid_module modules/mod_cgid.so
MaxRequestWorkers 2000
</IfModule>

I'm am using Plesk Onyx and server specification are following.

Processor: Intel Xeon E5-1620v2 - 4c/8t - 3.7 GHz/3.9 GH

Sever Ram: 64GB DDR3

Then I have tried the following settings

<IfModule mpm_event_module>
StartServers                80
MinSpareThreads             50
MaxSpareThreads             300

ThreadLimit                 25
ThreadsPerChild             25

ServerLimit                 500
MaxRequestWorkers           2000
MaxConnectionsPerChild      0
</IfModule>

but issue remain un solved, infarct its generating more errors & log-writer started eating CPU

output of httpd -V | grep -i 'version\|mpm' is following

Server version: Apache/2.4.6 (CentOS)
Server MPM:     event

Solution

ServerLimit is not defined/not read, but still that value you want to try makes no sense since threads per child is already forcing the serverlimit to 80.

And why do you use so small number of threads? You are generating too many child processes without need, probably making Apache less performant in the process (spawn processes more expensive than threads)

Note: MPM settings require a FULL STOP/START (not restart).

Set this.

StartServers 1
ServerLimit 4
MinSpareThreads 500
MaxSpareThreads 1500
MaxRequestWorkers 2000
ThreadsPerChild 500
ThreadLimit 500
MaxConnectionsPerChild 0
MaxKeepAliveRequests 1500
KeepAlive On
KeepAliveTimeout 10

And do make sure you do a full stop then start for the changes to be applied for real.

Comments

[Admin]

If you want MaxRequestWorkers of 2000, the ServerLimit only needs to be 25. Setting it to 500 may be overpowering your system. See the ServerLimit directive documentation

[Admin]

You also don't need to start all 80 servers right off

[Admin]

@Colt could you suggest / optimize my values for high traffic site?

[Admin]

See performance tuning documentation for MaxRequestWorkers formula, and the MPM core and event documentation for other settings

[Admin]

@Colt I have tried it but results are not good. I have write the conf I have tried in my question. I think performance tuning need experience so I am asking to help me out please

[Hassaan]

Thank you so much for response. Yeah actually I don't much knowledge and experience in performance tuning of apache 2.4. I have applied your suggested setting and things seem OK but When I hit ab -n 100000 -c 500 http://www.4songs.pk/ command to test server, my site works to slow. I have good processor and ram. What do you suggest is these setting are OK?

[Hassaan]

Do I need other setting like EnableSendfile or KeepAlive connections to increase performance ?

[ezra-s]

I would also encourage to upgrade from 2.4.6 , it's quite an old version.

[Hassaan]

yes I want to upgrade this one but I affair it does not support working because yum update does not show new version of apache.

[ezra-s]

too small number of maxkeepalive if you want to allow a max of 2000 workers imo, try the 80% rule.

[ezra-s]

there you have it.

[Hassaan]

Thank you. I read somewhere KeepAlive KeepAliveTimeout MaxKeepAliveRequests are not used on MPM Events is this true?

[ezra-s]

no, that's false

[Hassaan]

Thank you, Can you help me out with this one serverfault.com/questions/843460/…

[Hassaan]

You can you please update your answer according to 5000 MaxRequestWorkers setting

[Hassaan]

You are expert in apache and I think you can help me out better