Re: Removing T/TCP and replacing it with something simpler

From: Sean Chittenden (sean_at_chittenden.org)
Date: 10/21/04

  • Next message: Mark Allman: "Re: Removing T/TCP and replacing it with something simpler" 
    Date: Thu, 21 Oct 2004 11:31:38 -0700
To: Andre Oppermann <andre@freebsd.org>

    > I intend to remove T/TCP (transactional TCP) support from our TCP
    > implementation for the following reasons:

    The special cases are evil.

    > However something like T/TCP is certainly useful and I know of one
    > special
    > purpose application using it (Web Proxy Server/Client for high-delay
    > Satellite
    > connections).

    Actually, there are two/three programs that I know of that use it.
    memcached(1), which found a fantastic decrease in its benchmarks.
    Here's an excerpt from the following link:

    http://lists.danga.com/pipermail/memcached/2003-August/000111.html

    > I benchmarked 3 different methods of doing network I/O:
    >
    > 1) the default way, with the Nagel algorithm.
    > 2) using TCP_CORK (Linux, same as TCP_PUSH on BSD)
    > 3) using TCP_NODELAY
    >
    > I measured both real time and number of packets on the wire.
    > The test was doing 2,500 deletes, sets, and gets, then a 2,500
    > get_multi.
    >
    > Seconds Packets
    > DEFAULT 102.48 22638
    > TCP_CORK 3.88 15105
    > TCP_CORK 3.87 15108
    > TCP_CORK 3.86 15105
    > TCP_NODELAY 3.99 20169
    > TCP_NODELAY 4.04 20170
    > TCP_NODELAY 4.00 20170

    and an internal reverse proxy server/modified apache that I've hacked
    together (reduces latency in a tiered request hierarchy a great deal,
    on order of the benchmarks from above).

    That said, I can't stress enough the usefulness of TCP_NOPUSH/ttcp(4).
    However it gets implemented, I don't really care. If ttcp(4) is ready
    to bite the dust, so be it, but extensions/options like this are
    fantastically useful to those who know about its existence/usefulness.
    Good luck with the replacement. :)

    In 2001, there was a push to make Linux's TCP_CORK option behave the
    same as FreeBSD's TCP_NOPUSH. Is maintaining that compatibility still
    a goal, or are we going to kick this change off to the Linux folk to
    have them play catchup (to what sounds like a more secure option than
    Linux's TCP_CORK)?

    http://seclists.org/linux-kernel/2001/Feb/0993.html

    -sc 

    -- 
Sean Chittenden
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  • Next message: Mark Allman: "Re: Removing T/TCP and replacing it with something simpler"