[JDEV] Detecting client/server disconnect?
oj at world.std.com
Tue Apr 10 09:17:20 CDT 2001
At 10:30 PM 4/6/01 -0700, Robert Temple wrote:
>This has been an minor issue for us.
It was minor for us too, until we switched over to handling our Jabber
connections through a load-balancer and it suddenly turned into a major
issue. That's because the load-balancer is aggressive about cleaning up
> People think they are connected
>or they think someone else is connected but really their socket connection
>was severed and the client and/or the server don't know about it. It
>sure would be nice if this was fixed in the protocol. I'm not sure how
>something like this would be backwards compatible...
The server-side keepalive I implemented does seem to be backwards
compatible. I believe the Winjab client-side keepalive is backwards
compatible -- hey, Winjab works fine!
> Is that important at this stage?
I believe this issue is tremendously important at this stage for the
(1) many corporate gateways (e.g. the ip masquerading stuff in Linux, and
SOCKS proxy servers) time out idle TCP flows in a few minutes.
(2) a scarce resource on any highly scaled up Jabber implementation is
sockets on the server. Even if you get up to 20,000 connections on a
single box, this amounts to $0.15 per connection if you pay $3000 for the
box (a typical price for a dual processor 800MHz noname Linux rackmount
with plenty of memory and spindle space). You want to scale to hundreds
of thousands of users? You can't waste connections.
With keepalive defined in the session-layer architecture, the
implementation of the server can scavenge idle ports and re-use them by
disconnecting sockets that haven't been heard from recently. You may be
able to get TCP keepalive to do some of this; that's fine.
This suggestion comes out of experience trying to scale up Jabber (using
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