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Date:      Mon, 10 Nov 2003 02:41:57 -0800
From:      Jonathan Mini <mini@freebsd.org>
To:        Andre Oppermann <oppermann@pipeline.ch>
Cc:        freebsd-net@freebsd.org
Subject:   Re: tcp hostcache and ip fastforward for review
Message-ID:  <823BFED0-136A-11D8-87D8-000A95CD3CF8@freebsd.org>
In-Reply-To: <3FAF5CD9.ADA58CAF@pipeline.ch>
References:  <3FAE68FB.64D262FF@pipeline.ch> <ACD9C291-12F7-11D8-87D8-000A95CD3CF8@freebsd.org> <3FAEC407.F10E7BA@pipeline.ch> <A740BB86-130A-11D8-87D8-000A95CD3CF8@freebsd.org> <3FAF5CD9.ADA58CAF@pipeline.ch>

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On Nov 10, 2003, at 1:39 AM, Andre Oppermann wrote:

> Jonathan Mini wrote:
>
> All in all I don't think it is worth adding this complexity.

I agree.

>> This is actually a small value for TCP connections which are being
>> used to forward messages, especially on gigabit links.
>> Heavily-intensive
>> web applications that are using small HTTP requests (pipelined inside 
>> a
>> persistent connection) to update small manipulations of state are
>> a good example of this.  I wouldn't be surprised to see chatter
>> between SQL servers follow similar patterns.  Applications which
>> use XML-based messaging often send several small packets per message,
>> which is unfortunate.
>
> Do you think such applications manage to send 1000 packets per second
> with less than 256 bytes payload per packet? I think the network code
> would collect some data to form a larger packet (unless TCP_NODELAY
> set)?

Traffic like that only happens when TCP_NODELAY is set.  Otherwise, you
get what you would expect.

>> On the other hand, I'm used to looking at proxies, which are not
>> the general case.  This is why the limits are tunable, after all. =)
>
> Is there way you could monitor such connections and compile some
> statistics how many small packets per second are sent? I could adjust
> the patch to just report the fact instead of dropping the connection.
> Could do it for 4.9-R too, it's fairly easy.

Alas, no.  This is from anecdotal experience from our support staff at
work.

-- 
Jonathan Mini
mini@freebsd.org
http://www.freebsd.org



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