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From Igor Galić <i.ga...@brainsware.org>
Subject Re: [users@httpd] MaxRequestsPerChild for worker mpm
Date Sat, 04 Dec 2010 00:30:41 GMT

Hi Rainer,

this was an amazingly terse and most of all: Excellent description.
Can I use it in the Performance documentation and/or the mpm docs?

So long,
i 

----- "Rainer Jung" <rainer.jung@kippdata.de> wrote:

> On 26.11.2010 19:20, Jonas Eckerman wrote:
> > On 2010-11-25 15:28, Igor Galić wrote:
> >
> >> Worker MPM will *never* spawn more than StartServers children.
> >
> > According to the docs at
> >
> <http://httpd.apache.org/docs/current/mod/mpm_common.html#startservers>
> > it will.
> >
> > Quote:
> > ---8<---
> > The StartServers directive sets the number of child server
> processes
> > created on startup. As the number of processes is dynamically
> controlled
> > depending on the load, there is usually little reason to adjust
> this
> > parameter.
> >
> > The default value differs from MPM to MPM. For worker the default
> is
> > StartServers 3. For prefork defaults to 5 and for mpmt_os2 to 2.
> > ---8<---
> >
> > The *ServerLimit* directive oth puts a hard limit on the numkber of
> > children Apache can start.
> >
> > Quote:
> > ---8<---
> > For the worker MPM, this directive [ServerLimit] in combination
> with
> > ThreadLimit sets the maximum configured value for MaxClients for
> the
> > lifetime of the Apache process. Any attempts to change this
> directive
> > during a restart will be ignored, but MaxClients can be modified
> during
> > a restart.
> > ---8<---
> >
> > More info at:
> >
> <http://httpd.apache.org/docs/current/mod/mpm_common.html#serverlimit>
> 
> StartServers and the spare directives configure the dynamics. As their
> 
> name indicates, how many processes are started, how many threads
> should 
> be idle minimum befoe sarting new processes and how many threads you 
> allow to idle before stopping processes.
> 
> The maximum number of connections that can be handled in parallel is 
> given by MaxClients. It is the most important parameter for sizing.
> Then 
> ThreadsPerChild defines how powerful each process will be, or in other
> 
> words, over how many processes the MaxClient threads will be 
> distributed. If you increase it, you will need less processes and if 
> modules use e.g. caches per process those will be more efficient. On
> the 
> other hand locking activity may increase and if you are using unstable
> 
> modules (crashes or leaks) more connections will break if one process
> 
> e.g. crashes.
> 
> The ServerLimit and ThreadLimit params only have to do with the
> ability 
> of dynamic reconfiguration the above using only graceful restarts, not
> 
> full restarts. During graceful restart the main Apache process is not
> 
> recycled. It needs to maintain a memory table with columns and rows fr
> 
> processes and threads inside processes. The size of the table needs to
> 
> be big enough for any ThreadsPerChild and (MaxClients /
> ThreadsPerChild) 
> you want to use.
> 
> So if no dynamic reconfiguration for those values is expected, you can
> 
> set ThreadLimit to ThreadsPerChild and ServerLimit to MaxClients / 
> ThreadsPerChild. If you plan to adjust ThreadsPerChild or MaxClients
> to 
> higher values later (using a graceful restart), you need to plan ahead
> 
> and set ThreadLimit and ServerLimit to the max values you expect to
> need 
> according to these formulas.
> 
> HTH.
> 
> Rainer
> 
> 
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-- 
Igor Galić

Tel: +43 (0) 664 886 22 883
Mail: i.galic@brainsware.org
URL: http://brainsware.org/

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