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From: Marc Slemko <marcs@znep.com>
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Subject: Re: sendfile(2) SF_NOPUSH flag proposal
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On Tue, 27 May 2003, Terry Lambert wrote:

> The overhead of toggling it would be costly.  However, I really
> don't understand why he isn't just not setting TCP_NODELAY in
> the first place, since it's an affirmative option, and then
> leaaving the socket alone to act like it's supposed to act.

Given the bug in FreeBSD's sendfile() that results in it sending
the headers in a separate segment, then just leaving Nagle enabled
will destroy your performance if you are implementing a protocol
such as HTTP with persistent (pipelined or not) connections due to the
interaction betwteen Nagle and delayed ack.

However, that is somewhat of a moot point for HTTP anyway because
if you support pipelined requests then for the most efficient
implementation of HTTP on the network layer you need to ensure that
the response headers and body from multiple requests can be coalesced
into the same packet.  When using sendfile(), this means you have
to control TCP_NOPUSH yourself, even if sendfile coalesced headers,
data, and trailers.

sendfile() still should be fixed to properly coalesce them.