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From davidmc <aranman...@gmail.com>
Subject Re: AMQCPP Openwire much slower than Stomp?
Date Tue, 24 Apr 2007 01:59:34 GMT

Just for the sake of correctness, the 40ms delay on Linux is not because of
Nagle's Algorithm; It's the "Delayed ACK timeout" time. It's the time that a
socket who just received a packet waits to send an ACK back if the process
who received said packet doesn't send anything back. The wait is to minimize
the number of packets in the network; if it can send some info in the same
packet as the ACK, all the better. But it's not going to wait forever; it
"only" waits 40 ms in Linux and 200 ms in Windows.

Nagle's algorithm waits for an ACK if the socket buffer is not full; but the
40ms wait here is not because of Nagle's algorithm directly, but because of
the ACK taking 40ms to arrive.
Nagle's algorithm can be disabled with TCP_NODELAY, but the "Delayed ACK
timeout" in Linux cannot be disabled or changed permanently, unless you
change the tcp code and recompile the kernel. 

Kindly

David


Teemu Torma wrote:
> 
> On Monday 23 April 2007, Mittler, Nathan wrote:
>> BTW, has anyone run the same test with a Java client to verify that
>> it is indeed an OpenWire thing and not an activemq-cpp specific
>> thing?
> 
> I have never timed Java client, but this is general networking issue and 
> how TCP works.
> 
> On linux, I see roundtrips <0.5ms if TCP_NODELAY is enabled both on 
> activemq-cpp and the broker, otherwise it is 80ms.  For some odd 
> reason, I sometimes see <0.5ms and 40ms timings, but rarely.  
> 
> This is pretty similar I have seen with stomp.  I have never actually 
> timed sending bunch of messages with openwire.  Maybe stomp effectively 
> sends messages asynchronously and openwire waits for ack for each 
> message?  (I have never looked what these protocols do).  
> 
> Setting TCP_NODELAY just on activemq-cpp the round-trip drops to 40ms.  
> The broker needs changing too to get consistent <0.5ms round-trip 
> latency.
> 
> For comparison omniORB, which we also use, sets TCP_NODELAY 
> unconditionally for all sockets.  
> 
> Btw, the delay on Linux for Nagle's algorithm is 40ms.
> 
> Teemu
> 
> 

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