[freetds] FreeTDS hangs when running a select

Hildo Biersma Hildo.Biersma at morganstanley.com
Tue Apr 8 08:05:44 EDT 2008

Brian Johnson wrote:
> We have a Windows system on the same network that uses the same firewall
> going through the same VPN tunnel.  The Windoze system works great (returns
> all the rows).  But both linux systems choke.  I'm truely stumped.  The log
> created when setting TDSDUMP did indeed seem to indicate that there was no
> problem, data just stopped flowing.  I also looked into the ODBC logs, and
> there was no clues there either.
> Any ideas?  Any where I can point a finger and say, "Aha!  I have something
> to update!"?
> For the record, I did try compiling .82RC4 but saw the same results.  So I
> am thinking you must be correct in that it's not FreeTDS.  :(

Check the selective ACK (SACK) network setting on your Linux system.  If 
you have a bad firewall, turning off SACK may help.

> -Brian
> On Mon, Apr 7, 2008 at 1:03 PM, James K. Lowden <jklowden at freetds.org>
> wrote:
>> Brian Johnson wrote:
>>> Let me start by saying that the following numbers are somewhat made up,
>>> but demonstrate the problem accurately.  Anyway, lets say we have a
>>> table with 5 columns, and 100 rows.  If we do a "select * from foo", we
>>> would expect to get 100 rows returned.  We don't.  Instead we get say 25
>>> rows, and the select hangs.  I can print out the results of those 25
>>> rows in perl, but the 26th row never gets returned.
>>> So, we modified the select to be "SELECT col1 FROM foo", and we got all
>>> 100 rows of that column.  So we did "SELECT col1, col2 FROM foo", and
>>> then we got 75 rows and it hung.  So we tried "SELECT col1, col2, col3"
>>> FROM foo", and ended up getting 50 rows.
>>> Of course, the numbers were not so nice and round.  As for how we are
>>> connecting, I have tried DSN and DNS-less connections with dbi::ODBC,
>>> and of course have tried with sqsh.  For sqsh I added an entry to
>>> freetds.conf, and then ran sqsh -S ENTRYNAME -U USER -P PASS.  I was
>>> able to do very small selects, but any time I did a select that returned
>>> large numbers of rows it hung.
>> There's nothing in FreeTDS that would explain what you're seeing.  It sure
>> sounds to me like there's something on your network -- perhaps a firewall?
>> Some sort of traffic shaper? -- between you and your server.
>> You can use TDSDUMP to create a log of the session and show it to your
>> network folks.  I think you'll see the server seems to stop sending in
>> mid-packet.  If you can show a successful log with the old server, that
>> might convince them to track it down.
>> HTH.
>> --jkl
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