Subject: Re: very slow TCP connection on localhost
To: Manuel Bouyer <>
From: Rui Paulo <>
List: tech-net
Date: 09/06/2006 14:58:18
On Sep 5, 2006, at 5:45 PM, Manuel Bouyer wrote:

> Hi,
> I've been tracking down a speed issue with an amanda backup. The  
> bottleneck
> seems to be a TCP socket between 2 processes on the backup server,
> which can transfers data at only a few 10s KB/s. netstat shows that  
> the
> receive queue on the reader side is always empty, while the send queue
> on the sender side is always full. ktruss shows that the reader  
> blocks on
> read on the socket, and can read one or 2 64k block per second.
> The writer blocks writing on the socket and can write only one or two
> 64k block per second. A tcpdump shows very bursty traffic on lo0, with
> long pauses. This really looks like a TCP issue to me, maybe  
> waiting for a
> timeout before sending ACK, or something like that.
> This is a 3.0_STABLE system from march.
> Attached is the output of tcpdump -w on lo0 for this TCP connection.
> Anyone has an idea about such behavior ?

So, if it's a TCP issue, you can reproduce this with ttcp/nttcp, right?

	-- Rui Paulo