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To: cygwin AT cygwin DOT com
From: jojelino <jojelino AT gmail DOT com>
Subject: Severe performance degradation of writev
Date: Mon, 07 Jul 2014 07:28:12 +0900
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2008-07-27  Corinna Vinschen  <corinna AT vinschen DOT de>

        * fhandler_socket.cc (fhandler_socket::send_internal): Send 
never more
        then 64K bytes at once.  For blocking sockets, loop until entire 
data
        has been sent or an error occurs.
        (fhandler_socket::sendto): Drop code which sends on 64K bytes.
        (fhandler_socket::sendmsg): Ditto.

This commit added workaround for KB823764. but it has brought another 
performance issue when writev sends <64k of data.
Execute following command shows the problem.
svnrdump dump --incremental http://svn.apache.org/repos/asf/subversion 
subversion
cygwin does split writev request into many WSASendTo call and serf 
library sets TCP_NODELAY for socket it uses, a WSASendTo call 
corresponds to a tcp packet.
You can see that http header is sent being splitted when you executed 
above command. Whereas win32 backend of apr library doesn't exhibit such 
behavior by using send call.
-- 
Regards.


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