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Re: Abandoned CVS server processes

From: Larry Jones
Subject: Re: Abandoned CVS server processes
Date: Mon, 4 Mar 2002 14:03:07 -0500 (EST)

Dan Peterson writes:
> While investigating an issue with CVS server processes (pserver v1.11), I
> noticed a number of processes that didn't appear to be talking to a client
> anymore and had been hanging around for many hours or even days.

What state does netstat say the connections are in?

TCP/IP has a problem with clients disappearing without correctly closing
the connection.  This is typically caused by a network outage, a system
crash, or a power failure (including someone turning off the power
without shutting the machine down first).  Because TCP/IP was designed
to allow network connections to survive temporary network failures, such
vanished clients are not detected quickly, and they may not be detected
at all.  If a server tries to send data to such a client, the lack of
ACKs from the client will eventually (typically a few hours) cause the
host system to declare the connection dead and inform the server
process.  On the other hand, if the server is waiting to read data from
the client, the fact that the client has disappeared will never be
noticed.  Most systems have implemented a "Keep Alive" mechanism where a
server can ask the system to periodically send a packet on otherwise
idle connections to detect vanished clients, but that takes longer to
declare the connection dead (up to a day or longer), not all systems
support it, and some systems appear to support it but don't really do
anything.  CVS uses it where it's available.

> Some of the processes had a parent process ID of 1 which tells me the
> process maintaining the network connection had exited and the process had
> been adopted by "init".

That indicates a bug in CVS.  It would be helpful if you could attach to
such a process with a debugger and get a traceback.

-Larry Jones

How many presents do you think I'd forfeit for just one
clean smack upside Susie's head? -- Calvin

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