Re: [WEB400] Persistent connections???

["Nathan M. Andelin" <nandelin@xxxxxxxxxxxxxxxxxxx>]

From: "David Gibbs" <dgibbs@xxxxxxxxxx>
> I need to find out if a persistent connection means that a connection is
> established with the remote http server and that same connection is
> maintained until closed by the client.

Persistent connections are a double edged sword.  On one side, they improve
network performance.  However, each connection locks an HTTP server thread.
When all the threads are locked, service is denied to new connections.  To
overcome that problem, one strategy is to increase the number of threads
that the HTTP server starts.  Normally that works well.  Threads are
lightweight.  Although active, they're usually in a wait state.

The problem is that it trashes a common CGI performance tuning trick, which
is to tunnel activations through as few server threads as possible.  For
example, if 100 HTTP server threads are available, and the site hosts 100
CGI programs, and the CGI programs run under a named activation group, then
the number of active CGI programs can grow to 10,000.  CGI programs that run
in a named activation group are never deactivated.  The only way to
deactivate them is to shut down the HTTP server.  Too many active CGI
programs will cause the system to thrash as programs are swapped in and out
of memory.

It's interesting to monitor HTTP server connections with the WRKTCPSTS
command.  With persistent connections turned on, the status rarely changes.
Otherwise new connections pop up and disappear as the display is refreshed.

Persistent connections pose a tuning dilemma, for some sites.

Nathan M. Andelin
www.relational-data.com