[rabbitmq-discuss] Huge latency in Linux, compared with Leopard

Bogon Choi bogon.choi at gmail.com
Sat Sep 27 21:38:42 BST 2008

I've learned a lot! I appreciate it.

Holger Hoffstätte-2 wrote:
> Matthias Radestock wrote:
>> Adding the line
>>     -kernel inet_default_listen_options '[{nodelay, true}]' \
>> to the options in the rabbitmq-server script does improve the results
>> significantly.
> Yay! Glad it helped.
>> So should we make TCP_NODELAY the default?
> That's difficult to decide, though IMHO it is probably the right thing to
> do for most common scenarios today. Ironically after I had found the
> problem I remembered that I had read something related on the Linux kernel
> list, where someone from RedHat was complaining about 40ms latency. :)
> Find the juicy details here:
> http://marc.info/?l=linux-netdev&m=122091100407930&w=2
> Other treads of interest may be:
> http://www.nabble.com/slow-tcp-acks-on-loopback-device-td464386.html
> http://www.nabble.com/What-happened-to-CONFIG_TCP_NAGLE_OFF--td7588964.html
> I also found that the Windows stack automatically turns Nagle off for
> loopback connections, and I assume other BSD-based OS (OS X) do as well.
> This would explain the platform-specific observations.
> Nagle makes sense in order to maximize bandwidth and prevent wasting
> packets for small payloads (~couple bytes, as for telnet) that can be
> packed together into one MTU. This may or may not make sense for Rabbit
> but is dependent on the network link and the payloads. So turning it off
> may be the right thing for localhost/LAN messaging where the cost of a
> single packet is low, but not at all for large(r) payloads and high
> bandwidth or slower tranports. I doubt that there are any people left who
> want to run over modem or carrier pidgeon..
> I am really looking forward to SCTP (as the lkml thread mentions) since so
> many of the underlying assumptions behind TCP have changed these days that
> no matter what the stacks try to do, it's always kind of wrong. Now it
> only needs to become stable..
> Holger
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> rabbitmq-discuss at lists.rabbitmq.com
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