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From Tom Evans <tevans...@googlemail.com>
Subject Re: [users@httpd] "client" or "request" meaning
Date Thu, 08 Mar 2012 15:12:50 GMT
On Thu, Mar 8, 2012 at 2:35 PM, Arianna Manlio <arianna.manlio@yahoo.com> wrote:
> Hi,
> sorry for previous message.
> I'm trying to fully understand the meaning of "client" or "request" concepts
> in Apache.
> For example:
>
> http://httpd.apache.org/docs/2.2/mod/mpm_common.html#maxclients
>
> Description:Maximum number of connections that will be processed
> simultaneously
>
> ...
> The MaxClients directive sets the limit on the number of simultaneous
> requests that will be served.
>
> So, what is a "connection"?
> If I connect to my home webmail, I see several connection, even if I the
> only user.
> This means that 5 or 6 "clients" are already reserved?
>
> Thankyou very much.
>

A client is an actor that makes requests. A user agent (eg a browser)
may have several simultaneous clients making requests.

When a client establishes a connection to the server, it is taking up
one slot. When it disconnects, the slot is then free again.

If the request is made with 'Connection-Type: Keep-Alive', then the
web server may choose not close the connection once it has sent the
response, and may wait for another request to be made over that
connection. For all MPM apart from event MPM, this will also take up a
slot. This behaviour is controlled by "KeepAlive" and
"KeepAliveTimeout" directives.

For the prefork MPM, you initially have "StartServers" slots. If there
are ever less than "MinSpareServers" slots, it will add another slot.
If there are ever more than "MaxSpareServers", it will remove a slot.
It will never have more than "MaxClients" or "ServerLimit" slots.

For the worker and event MPM, you initially have "StartServers" *
"ThreadsPerChild" slots. If there are ever less than "MinSpareThreads"
slots, it will add an additional "ThreadsPerChild" slots. If there are
ever more than "MaxSpareThreads", it will remove "ThreadsPerChild"
slots. It will never have more than "MaxClients" or "ServerLimit" *
"ThreadsPerChild" slots, whichever is smaller.

If you are using winnt MPM, ask someone else!

A good way to understand this is looking at the text scoreboard
representation on the mod_status server-status page.

Cheers

Tom

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