Re: Help me in setting up MaxClients

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On Mon, Jan 25, 2010 at 6:13 PM, Vikrama Sanjeeva
<viki.sanjeeva@xxxxxxxxx> wrote:
> Hi Jeff,
>
>     Below is statistics from vmstat while everything is running including
> httpd:
>
>>> vmstat 2 3
>  kthr      memory            page            disk          faults      cpu
>  r b w   swap  free  re  mf pi po fr de sr rm s0 s1 s3   in   sy   cs us sy
> id
>  0 0 0 32953272 20946824 11 22 0 3 3  0  0 -0  0  1 -0  872 1041  601  0  0
> 100
>  0 0 0 23225344 11281392 51 104 0 0 0 0  0  0  0  3  0 1024 1767  684  0  0
> 100
>  0 0 0 23224768 11280792 1 4 0  0  0  0  0  0  0  0  0  892 1080  473  0  0
> 100
>
> So with this, I have:
> Free Swap: 22  GB
> Free RAM: 10 GB
>
> Here I am doing a defensive supposition by assuming 5/10 GB of Free RAM
> "could be" occupied by future applications (if any). So, I am left with 5 GB
> of Free Memory. Same for Free Swap, assuming I am left with 5 GB Free Swap
>
> Putting values in MaxClient Formula:
>
> MaxClient = (RAM Size - some room for other processes) / Avg
> HTTPD Process Size
>
> MaxClient = (32768 - 27648) / 12 = 426 (approx)
>
>   Does it mean, I can set MaxClient value to 426 ? If yes, then:

yes, 426 is very safe as far as RAM goes

(as I mentioned before, 12MB is in excess of the per-process RAM
requirements, so I expect you could go much higher; unfortunately I
don't have clear instructions on how to use pmap or other tools to
find the real per-process RAM requirements)

also confirm that 12M * 426 is less than the available swap space

>
> (i) I have to make sure ServerLimit is also = 426  [As per your presentation
> for MPM prefork] ?

y

> (ii) Make sure backend server node (tomcat AJP port) can accept 426
> concurrent requests ?

the big picture for that part of the presentation is to consider the
relationship between number of connections hitting Apache and number
of clients hitting the backend (e.g., Tomcat)

if every connection that hits Apache gets forwarded to Tomcat, you
should align the capacity of Apache and Tomcat fairly closely

if only some connections that hit Apache get forwarded to Tomcat,
you'd expect that the capacity of Apache should be much larger than
that of Tomcat

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