No need to worry. 

I run REST requests through Varnish box > nginx / Tornaod / Python box > Cassandra cluster and can get requests in and out of the stack in a couple of milliseconds. Using some old workstation HW and not paying much attention to tuning. 

Build it like a normal system and separate out the parts, if / when you have problems then you can look at tuning the cassandra cluster or other parts of the stack. There are normally a number of other issues to deal with before network IO.

Hope that helps. 
Aaron


On 17 Nov, 2010,at 03:31 PM, E S <tr1sklion@yahoo.com> wrote:

I am considering building a system as follows:

1. Data stored in Cassandra
2. Webservice cluster (stateless) will pull data from cassandra and do business
operations plus security enforcement
3. Clients will hit the webservice cluster

I'm trying to maintain a low read latency and am worried about the number of
hops. Client will hit the webservice. The webservice will hit a random node in
the cassandra cluster. The cassandra cluster will then route the the
appropriate node and the data will flow all the way back.

How many of these hops can I remove? I would bundle the cassandra and
webservice processes onto each box. If I route the webservice to always go to
the local node, I'll remove one hop. Is it possible to optimize this further so
that the client can use the cassandra routing logic to go to the webservice that
also houses a cassandra node that contains the data? In this case, there would
only be one hop, and if the data is used frequently, I it will likely reside in
memory without requiring a separate caching layer. This is an internal
webservice, so I would be ok with a library on the client side to help with the
routing.

Is any of this possible? I was looking at the cassandra apis and couldn't
figure out a way.

Thanks for any help!