Re: Socket open overhead?

On Mon, 26 Apr 2004, David Gibbs wrote:
>
> Anyone know how much overhead there is in opening & closing a socket?
>

What do you mean by "opening and closing?"  Are you including the time it
takes to connect and/or disconnect in that?

There is some overhead in calling the socket() API to create a new socket.
There's also some overhead in calling the close() API to delete that
socket -- but that overhead is relatively small when you compare it to the
time it takes to connect to a host and/or disconnect from that host.

(and, perhaps confusingly, the close() API both disconnects and deletes
the socket descriptor -- depending on the state of the socket...)

> I'm in the process of working with a socket interface that requires that
> I open a new socket for each request, shut the socket down when I am
> done sending, and close the socket when I am done receiving.
>
> Any thoughts on if this is especially inefficient?

It really depends on the application.  Take a telnet application for
example...  the user has to connect/disconnect for each request -- but the
requests can last hours, so the connect/disconnect time is insignificant.

On the other hand, consider an HTTP application.  Each time you switch web
pages, the browser will open up potentially dozens of connections to the
server, download a few kilobytes of data and disconnect.  In that
situation a persistent connection saves a bit of time.  (Which is why
persistent connections are the default in HTTP 1.1)

In other situations, TCP just isn't the right choice.  I've got an
application that sends records from a PC on the manufacturing floor to the
iSeries.  The project specs call for each 128 byte record to be sent
individually to the iSeries.  That 128 bytes takes only a fraction of a
second to send over the network, but there are 20 programs sending them at
any given time, and thousands are being sent every hour.   In this case,
building a new TCP socket, connecting, sending and disconnecting would be
horribly inefficient.   Instead, I use the UDP protocol which doesn't
require creating new sockets or making connections -- I build one UDP
socket and send many records (each as it's own individually tracked
datagram)  Since UDP is connectionless there's no need for the
overhead of connecting & disconnecting.