E3-1240 with 32GB Ram - Unable to set the optimal value for the server

Peter Booth peter_booth at me.com
Wed Oct 18 00:16:41 UTC 2017


I work as performance architect , specializing in improving the performance 
of trading applications and high traffic web sites. When I first began tuning 
Apache (and then nginx) I realized the the internet was full of “helpful suggestions” 
about why you should set configuration X to this number.
What took me more than ten years to learn was that 95% of these tips are 
useless,  because they are ideas that made sense in one setting 
at one time that got copied and passed down year after year without people 
understanding them. So be skeptical about anything that anyone suggests, including me.

Regarding one of these settings: max_requests.
This is a very old setting inherited from apache that originally allowed you to 
recycle apache worker processes after they had handled N requests. 

Why would you do this?

If your worker included a module that leaked memory then over time worker processes
 would grow in size - this setting would mean that each worker would get killed eventually, 
at different time, so a new fresh process could be started to take its place, avoiding a 
catastrophe where all of your your workers consume all the memory on the host.

In 2017 you can absolutely set iit to zero, provided you keep track of the size of your processes.
In fact we can confirm this idea just from your top output. 

3135 nginx     20   0  393108  12112   3832 R   7.3  0.0  10:30.35 php-fpm: pool www
6839 nginx     20   0  392804  11832   3828 R   7.3  0.0  10:37.57 php-fpm: pool www

See how process 3135 has been running fro 10 minutes 30 seconds whilst process 6839 has been running for 10 minutes 37 seconds.
But the longer running process has a smaller resident set size (RSS = memory in use)

If you look at all of the lines its easier to see that there is no trend of memory increasing over time:

NewiMac:Records peter$ cat phpOutput.txt | grep php-fpm | awk '{print $11,$6}' | head -15 | awk '{print $2}' | average -M
NewiMac:Records peter$ cat phpOutput.txt | grep php-fpm | awk '{print $11,$6}' | tail -15 | awk '{print $2}' | average -M

> On Oct 17, 2017, at 12:39 AM, agriz <nginx-forum at forum.nginx.org> wrote:
> Sir reading some info, i guess i cant tell any number blindly without test.
> I think 
> I can first try to give these values
> max_children = 100
> start server  = 34
> spareserver min and max = 20 & 50
> We have around 20GB free Ram all the time. Why can't we use it for php-fpm?
> Are those values safe to check?
> But max_requests, why should we limit the numbers to 500 or 2500? Why cant
> we have unlimited? What is wrong in setting it to zero?
> Posted at Nginx Forum: https://forum.nginx.org/read.php?2,276892,276907#msg-276907
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