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From Sander Temme <scte...@apache.org>
Subject Re: [users@httpd] Info when the MaxClient is reached
Date Mon, 02 Apr 2007 05:19:00 GMT
Hi Arnab,

On Apr 1, 2007, at 9:53 PM, Arnab Ganguly wrote:

> Want some info when the MaxClient value is reached, what would  
> happen to Apache webserver?Is that particular of time if we ping  
> apache it will time out.How long will it take to recover or the  
> requests will be queued?
> Can you tell me is there any configurable parameter in NES similar  
> to MaxClient settings in Apache.ie the max simulatenous request it  
> can handle?

The MaxClients directive dictates the maximum number of child  
processes (prefork) or worker threads (other MPMs) Apache can spawn.   
Its name is slightly misleading: MaxClients does not actually dictate  
the maximum number of clients that can connect to the web server.  It  
does, however, dictate the maximum number of requests Apache can  
handle concurrently.

As TCP connections arrive on Apache's listening socket, they are  
queued by the kernel.  All the Apache workers receive these TCP  
connections in the order in which they arrived.  If Apache handles  
the requests fast enough, the queue will be mostly empty and any new  
connection will be received by an Apache worker immediately.  If the  
server is busy, requests may queue up and the client's browser will  
say 'Connecting to... ' in the status bar.  The number of connections  
that can queue up is platform-specific, but you can manipulate it  
using the ListenBacklog directive:

http://httpd.apache.org/docs/2.2/mod/mpm_common.html#listenbacklog

Only when the kernel's queue is full, and all Apache children are  
busy will the server refuse new incoming connections, and the way in  
which this happens also depends on the server platform.

Of course all of this happens on the Apache listening socket, and has  
nothing to do with ping (ICMP) which is handled completely inside the  
kernel.

S.

-- 
sctemme@apache.org            http://www.temme.net/sander/
Open Source Software Consultant
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