[users@httpd] Broken pipe erros causing high system load

["Abfalterer, Armin" <Ar...@united-security-providers.ch>]

Hi all,

I have encountered a performance problem (high system load, slow
response times) when making lots of requests that drop the TCP
connection while reading the response. That is, a client reads some
bytes of the response and cuts the transmission with a TCP RST.

In my tests I have used 100 concurrent clients that force the problem in
an infinite loop and bring the server on his knees. In the error_log of
the Apache I see lots of "(32)Broken pipe: core_output_filter: writing
data to the network" errors. The number of sockets in TIME_WAIT state
increases explosively.

I use a relative high dimensioned Apache/2.2.17 with MPM worker on a
Linux server (quad-core@2.33GHz, 8GB RAM). The most important settings
are following:

------
ServerLimit 64
StartServers 32
MaxClients 1024
MinSpareThreads 512
MaxSpareThreads 512
ThreadsPerChild 16
MaxRequestsPerChild 1000000

Timeout 3
KeepAlive                    on
MaxKeepAliveRequests         10000
KeepAliveTimeout             5

EnableSendfile Off
EnableMMAP Off

HostnameLookups              off
------

Anyone who can confirm the problem? Is this a problem in Apache or is it
related with the OS (TCP/IP stack)?

Regards, Armin