FreeTDS Development Group

["martin A." <acevedoma AT hotmail.com>]

Hello, thank you for your help, I will try to put some expiration time in 
minutes, after that I consider the conecction is dead, I do not know very 
much about sockets and tcp programming...




> From: "Pickett, David" <David.Pickett AT phlx.com>
> Reply-To: FreeTDS Development Group <freetds AT lists.ibiblio.org>
> To: 'FreeTDS Development Group' <freetds AT lists.ibiblio.org>
> Subject: Re: [freetds] Connection life
> Date: Fri, 25 Nov 2005 10:22:51 -0500
>
> TCP will send a FIN packet if the remote end closes a socket.  Keepalive, 
> if
> turned on and not subverted by router traffic reduction faking, will
> eventually time out for 100% packet loss.  Either will raise an error or 
> EOF
> condition that read(), write(), poll(), if configured to accept all events,
> and probably select() (I know poll better, but they are generally
> equivalent) will notice on the local socket fd.  I am not sure if the 
> remote
> close comes up as an error event, a read event or a write event, but it
> comes up.
>
> Similar things happen with pipes.  Generally, you cannot check to see if a
> remote pipe reader has closed by sending a zero length message, as most
> readers take this as EOF (read() returns zero).  Maybe there is an out of
> band message you can use that does not upset simple readers; I have tried 
> to
> live the simple life, without knowing much about the funny messages on a
> stream.
>
> At the TCP level, an empty message is an ack or keepalive message. (Both 
> are
> identical in content but different in triggering mechanism.)  I am unsure 
> if
> it always produces an event.  However, on the rumor of past woes, I have
> coded some socket apps to declare EOF only for N consecutive read()=0
> responses within a second (a real EOF will repeat N times relatively
> immediately, but TCP ack/keepalive timers run at much longer intervals).
> Nobody said it would be easy!
>
> Of course, an up connection does not mean the server is viable -- it might
> be hung and ignore activity on its sockets.  You can only tell by 
> requesting
> some sort of service.
>
> -----Original Message-----
> From: ZIGLIO, Frediano, VF-IT [mailto:Frediano.Ziglio AT vodafone.com]
> Sent: Thursday, November 24, 2005 3:03 AM
> To: FreeTDS Development Group
> Subject: Re: [freetds] Connection life
>
>
> >
> > Hello, I have a question about connection and disconnection.
> > How can I
> > detect if a network connection is dead using db-lib? I have
> > seen that there
> > is a function called  dbdead, but this function does not
> > check  if the
> > network socket is alive ( I use  MS Sql Server), it never
> > connects to the
> > server... I need this because I have a connection pooling and
> > I havte to
> > detect connections dead to reconnect if it is needed, I keep
> > the connection
> > without calling a dbclose for a long time. But if the dbdead
> > does not check
> > the socket the result of calling dbdead is not reliable.
> > How can I solve this problem?
> >
> > Thanks...
> >
>
> I don't know if even tcp support this. Current version use keep alive in
> socket but I don't know if there is a way to read error like using
> select on error with timeout == 0 or use recv with zero bytes or reading
> error with getsockopt/SO_ERROR...
> However I would suggest to close connections if they are idle for a long
> time (some minutes), closing unused connection can free memory on mssql
> side and prevent potential locks.
>
> freddy77
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