Hello All:
I've been requested to add some TCP tuning parameters to some CentOS 5.4 systems. These tunings are for the TCP receive buffer windows:
net.core.rmem_max net.core.wmem_max
Information on this tuning is broadly available: http://fasterdata.es.net/TCP-tuning/linux.html http://www.speedguide.net/read_articles.php?id=121
Potential downsides are available: http://www.29west.com/docs/THPM/udp-buffer-sizing.html
From the above, the rmem size is a function of the number of listening
processes times the size of the receive buffer.
Apache can initially create a bunch of server processes (StartServers directive, for example). In our environment we may spawn off 50 or more httpd listeners. Does each listener allocate its own buffer or is the parent process the only one?
The tunable seems innocuous but I am concerned about the impact to memory given that there will be many listener processes. We are running fairly tight already and because these are virtual environments in a cluster, adding a meg or so per listener can equate to multiple gigs across all the machines in the virtual host cluster.