[freetds] FreeTDS hangs when running a select

James K. Lowden jklowden at freetds.org
Tue Apr 8 10:03:40 EDT 2008

Brian Johnson wrote:
> The Windoze system works great (returns
> all the rows).  But both linux systems choke.  

Consistent with a network issue, pointing to the firewall.  :-/

> The log
> created when setting TDSDUMP did indeed seem to indicate that there was
> no problem, data just stopped flowing.  ...
> Any ideas?  Any where I can point a finger and say, "Aha!  I have
> something to update!"?

You may find that something simple, say, ftp, fails if the file is large
enough.  That would eliminate the whole application layer and focus
attention on the network.  

In case Hildo's selective ACK suggestion doesn't do the trick, the
technical path would be to use tdsdump(8) to log the connection, and watch
the server stop sending when it shouldn't.  For extra credit, scope the
server's side, too.  It's work, and some shops don't have the chops.  With
luck you'll find either the "stuck" packet, the one the server sent that
the client never received, or you'll see the server mysteriously stop
sending even though the client is waiting and has abided by the TCP/IP

(Windump works pretty well if you have the tcpdump man page handy, but I
have  never used it with a VPN.)

Lament: Observe the negative network effect of Windows.  Your firewall
"works great" with the Windows machines, but not with Linux.  Your choice
is to fight or switch, and fighting requires knowledge and patience ...
and possibly new VPN software.  Who can blame the person who looks at that
scenario before it even begins, and decides not to go there?  

Anyway, good luck.  Please post the outcome if you would.  Someone else
might benefit.  


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