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freetds - Re: [freetds] No Earthly reason for MARS

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  • From: Peter Deacon <peterd AT iea-software.com>
  • To: FreeTDS Development Group <freetds AT lists.ibiblio.org>
  • Subject: Re: [freetds] No Earthly reason for MARS
  • Date: Sun, 22 May 2011 19:06:39 -0700 (Pacific Daylight Time)

On Sun, 22 May 2011, James K. Lowden wrote:

http://www.freetds.org/mars.html

A little explanation of what I see as the problems inherent in MARS and
why it's bad for TDS and FreeTDS, even if it's necessary to maintain an
ODBC driver compatible with Microsoft's. I thought it would be better
to state my case plainly, where it can be evaluated and corrected, than
to make occasional snide comments as we slouch our way there. Maybe
someone will even write a unit test to measure the "MARS tax".

FWIW tend to agree on network side.

My guess depending on network conditions (esp high RTT WAN/Intl links) at some point you are much better off with a connection pool of multiple real TCP sessions and shared session/transaction context (sp_bindsession) vs MARS.

No matter how good the protocol if you start multiplexing within a single TCP stream you are still limited by the head-of-line blocking nature of TCP.

With low RTTs MARS may significantly reduce concurrent TCP session counts at little to no cost and folks writing code for heavily async environments might tend to appreciate MARS more than those of us used to a synchronous environment.

regards,
Peter




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