FreeTDS Development Group

["Lowden, James K" <LowdenJK AT bernstein.com>]

> From: ZIGLIO, Frediano, VF-IT
> Sent: Tuesday, March 15, 2005 7:14 AM
> 
> > > You tested that TCP_NOPUSH under FreeBSD 5.0 do not work 
> > correctly so
> > > would be so kind to try with
> > 
> > > /* Try to use TCP_CORK on *BSD */
> > > #elif (defined(__FreeBSD__) || defined(__GNU_FreeBSD__) ||
> > > defined(__OpenBSD__)) && defined(TCP_CORK)
> > > #define USE_CORK 1
> > 
> > Hi Freddy,
> > 
> > That works fine on my FreeBSD 5.0 system.
> > 
> > FWIW here are the avaliable options from tcp.h
> > 
> > #define TCP_NODELAY     0x01    /* don't delay send to 
> > coalesce packets */
> > #if __BSD_VISIBLE
> > #define TCP_MAXSEG      0x02    /* set maximum segment size */
> > #define TCP_NOPUSH      0x04    /* don't push last block of write */
> > #define TCP_NOOPT       0x08    /* don't use TCP options */
> > #endif
> > 
> 
> So I think is working using NODELAY option... do you know a way to
> "emulate" linux CORK behavior, that is coalesce packets and flush them
> when needed ??

This might be helpful: http://dotat.at/writing/nopush.html.
http://www.kegel.com/c10k.html#writev recommends writev(2) over
TCP_CORK.  

I have a basic question: Why are we doing this?  It's the TCP stack's
job to decide when to flush packets.  Why should we worry about such
low-level, implementation-dependent, nonstandard details?  Unless the
timeout is very long, the advantage of coalescing frames ISTM is very
small, particularly in light of portability issues.  

I can see the advantage of TCP_NODELAY, given how often TDS sends small
packets.  I don't see the advantage in using less widely implemented
options.  

Is there a measurable difference with tsql or freebcp?  

--jkl



-----------------------------------------
The information contained in this transmission may contain privileged and 
confidential information and is intended only for the use of the person(s) 
named above. If you are not the intended recipient, or an employee or agent 
responsible for delivering this message to the intended recipient, any 
review, dissemination, distribution or duplication of this communication is 
strictly prohibited. If you are not the intended recipient, please contact 
the sender immediately by reply e-mail and destroy all copies of the original 
message. Please note that we do not accept account orders and/or instructions 
by e-mail, and therefore will not be responsible for carrying out such orders 
and/or instructions.
If you, as the intended recipient of this message, the purpose of which is to 
inform and update our clients, prospects and consultants of developments 
relating to our services and products, would not like to receive further 
e-mail correspondence from the sender, please "reply" to the sender 
indicating your wishes.  In the U.S.: 1345 Avenue of the Americas, New York, 
NY 10105.