Conference turris::digital_unix

10039.0. "limit on socket connections" by HYDRA::DORHAMER () Wed Jun 04 1997 11:49

We are performing a test on Digital UNIX v4.0B with a partner application 
(Progress) to determine how many connections can be made to their database.  
Clients connect to a database on a server via tcp/ip.  We are reaching a limit 
in terms of the number of socket connections that can be made.  At about 3900 
connections, an error is received on a connect call which says that the socket 
is already connected.  At this point, the system locks up for a few seconds
and the message "Address already in use" is received due to an error received
on the connect call.  The error does not make sense since the connections
are always to a new socket.

Are there some kernel tuning parameters that need to be increased?  We have
already increased many of the ipc, proc and vm parameters (see attached listing
of parameters that have been set in the sysconfigtab file).  A test case 
which reproduces the problem can be found in the anonymous ftp area on
fluid.mro.dec.com in a tar file named socketbug.tar.  The README
file explains how to run the test case.

Thanks,
Karen Dorhamer
Software Partner Engineering

sysconfigtab parameters:

vmunix:
	maxusers = 1024
proc:
        max-proc-per-user = 1024
        max-threads-per-user = 4096
        max-per-proc-address-space = 0x10000000000
        task-max=4096
        thread-max=200000
ipc:
        set-max-num = 0x100000
        max-kernel-ports = 65500
        sem-mni = 0x1000
        sem-msl=65535
        shm-max=1073741824
        shm-seg = 0x1000
        shm-mni = 0x1000
        sem-opm=65535
        sem-ume=65535
        sem-vmx=65535
        sem-aem=65535
        num-of-sems=65535
vm:
        vm-maxvas = 0x10000000000
        vm-mapentries = 400
        gh-chunks=0
        vm-segmentation=1
        gh-fail-if-no-mem=0
inet:
        tcpnodelack=1
    

    The user reserved port limit is 5000, minus the reserved
    ports (1-1024).  So, there are only 3975 ports available
    for outgoing connections from a Digital UNIX client.
    
    There is a dbx tunable called ipport_userreserved which
    you can increase, all the way to 64K, which is the limit.
    Just dbx -k /vmunix and assign it to 65535.  There is no
    need to reboot, it takes effect immediately.
    
    This tunable is in sysconfigtab, but not until the V4.0D
    release.  We have seen a number of proxy situations running
    into the user reserved port limit, hence the need for this
    to be tunable.
    
    John