Question

All the examples I’ve seen of sock.listen(5) in the python documentation suggest I should set the max backlog number to be 5. This is causing a problem for my app since I’m expecting some very high volume (many concurrent connections). I set it to 200 and haven’t seen any problems on my system, but was wondering how high I can set it before it causes problems..

Anyone know?

Edit: Here’s my accept() loop.

while True:    
    try:
        self.q.put(sock.accept())
    except KeyboardInterrupt:
        break
    except Exception, e:
        self.log("ERR %s" % e)

Answer 1

The doc say this

socket.listen(backlog) Listen for
connections made to the socket. The
backlog argument specifies the maximum
number of queued connections and
should be at least 1; the maximum
value is system-dependent (usually 5).

Obviously the system value is more than 5 on your system. I don’t see why setting it to a larger number would be a problem. Perhaps some memory is reserved for each queued connection.

My linux man page has this to say

If the backlog argument is greater than the value in
/proc/sys/net/core/somaxconn, then it
is silently truncated to that value;
the default value in this
file is 128. In kernels before 2.4.25, this limit was a hard coded value, SOMAXCONN, with the value 128.