min spare servers Directive

Hi
We are using prefork apache on Red Hat Enterprise Linux AS 
4 with the
following settings:
 
MaxKeepAliveRequests 100

KeepAliveTimeout 15

<IfModule prefork.c>
StartServers       8
MinSpareServers    8
MaxSpareServers   300
ServerLimit      575
MaxClients       575
MaxRequestsPerChild  4000

What I am unclear about is that if the server limit is 575
and I have
actually reached this limit will there be 8 additional
children
started(MinSpareServers) that is not serving requests but
will be if any
of the other children stops or reaches MaxRequestsPerChild?


When I do a character count on server-status I get the value
of 584
which confirms my above reasoning.

This apache httpd server is used to front 12 Tomcat servers
using
mod_jk.

I think the MaxSpareServers value is a bit high. I believe
the original
reasoning behind this value has been because we receive
regular burst of
traffic and then it is better to have apache keep the
processes active
to sit out the burst of traffic. 

We have also considered changing the parameters as follows
to improve
performance after a httpd restart which unfortunately at the
moment is
fairly often:

StartServers       16
MinSpareServers    16
MaxSpareServers   64

Any opinions on these values would be appreciated.

Regards

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On 28/08/07, Gerhardus.Geldenhuisgta-travel.com
<Gerhardus.Geldenhuisgta-travel.com> wrote:
> What I am unclear about is that if the server limit is
575 and I have
> actually reached this limit will there be 8 additional
children
> started(MinSpareServers) that is not serving requests
but will be if any
> of the other children stops or reaches
MaxRequestsPerChild?

That would seem pointless.. Why keep children around
(consuming
memory) when old ones can be reused once a request is
finished when
MaxClients is reached?

As I understand it, at MaxClients, new requests get queued
by the OS,
up to the limit set by
http://httpd.apache.org/docs/2.2/mod/mpm_commo
n.html#listenbacklog

I don't run any sites that get that especially busy.
Hopefully
somebody will correct me if I'm spouting nonsense.

-- 
noodl

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