It was thus said that the Great Mick Sheppard once stated:
> Hi,
>
> Just to throw a slight spanner in the works here. My understanding of
> 'open files' is open file descriptors. As far as a file descriptor is
> concerned there is no real difference between a physical file on disk
> and a socket (network connection). So eliminating physical files, whilst
> it might get you a little more headroom, is unlikely to solve the
> problem.
Yes and no. Yes, sockets are considered "opened files" and do count
against the open file limit, that limit is *per process*, not *system wide*.
I just checked one of our main web servers (serving up a few hundred sites)
and found only three active sockets per process:
1. the listening socket on port 80, waiting for a connection
2. the listening socket on port 443, waiting for a connection
3. an actual connection to a client
The main root process only has the first two sockets open. If you have
Apache configured to have at a minimum 30 spare servers, no one Apache
process will have 30 sockets open---sockets just don't work that way. What
it does mean is you have at least 31 apache processes running, one as root
(to bind to the proper ports [1]) and 30 ready to service a request, so at
most, any Apache process will have one socket per Listen statement, and one
socket only when actually processing a request.
So, for example, let's say you have the following Apache configuration:
Listen *:80
StartServers 100
MinSpareServers 100
MaxSpareServers 900
ServerLimit 1000
MaxClients 1000
MaxRequestsPerChild 4000
CustomLog access_log
ErrorLog error_log
All your apache processes would have only seven files open (eight if serving
a request), and they would look something like:
0 -> /dev/null (STDIN)
1 -> /dev/null (STDOUT)
2 -> error_log (STDERR)
3 -> listening socket
4 -> pipe (for CGI communications)
5 -> pipe (for CGI communications)
6 -> error_log
7 -> access_log
The real concern are log files, not the number of connections in the
Apache configuration. The only way the number of connections might be a
consideration is if you are using the threading MPM, where each thread (in a
single process) gets a connection.
> Remember that as you add connectivity to databases that this will
> increase the number of sockets, and therefore open files, used for each
> page served.
True, but you really need to look at this at the process level.
-spc
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