[c-nsp] Application Protocol Performance in low latency envrionments

[Mikael Abrahamsson]

On Wed, 26 Aug 2009, Ash Net wrote:

> The reason for performance degradation solely seems to be latency 
> related since there's tons of b/w available in the lab setup and over 
> 10G lanphy paths. Do people still deploy QOS for better traffic 
> management on the lanphy interfaces even with no saturation?.

All the protocols you mentioned are "query/response" ones and thus they 
take a big hit when latency is introduced.

I know several companies who nowadays has a wan simulation device between 
the clients and servers in their dev labs, just so that the developers 
will develop applications that actually work in real life, not just in the 
1/10 ms latency of the dev environment. Imagine the difference in a 
latency environment between doing a single nested SQL query, as opposed to 
doing 1 returning a list, and then doing one query per list entry. In a 
1/10ms environment the difference might not be noticeable, but in a 100ms 
environment it most certainly will.

At several ms network latency you're effectively dealing with harddrive 
latencies as opposed to almost memory latencies, and thus techniques that 
work akin to NCQ or alike needs to be employed. Failure to do so will 
create performance problems in real life.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se