Once the cluster has returned to the client you know the write has been committed to Consistency Level  number of nodes. 

i.e. If you send an insert using QUORUM consistency to a cluster with Replication Factor 3, and you get a non error response you know the write has occurred on at least 2 nodes (one may be the one the client is connected to.)

After the initial request has completed it's up the "Eventual Consistency" features of Read Repair, Hinted Handoff and Anti-Entropy to distribute changes. 

Does that help or are you thinking of something else?  
Aaron Morton
Freelance Cassandra Developer

On 25 May, 2011,at 03:11 PM, Stephan Pfammatter <steplmi4124@gmail.com> wrote:

Whatís the recommended way of measuring latency between nodes in a cluster?

By that Iím not referring to read/write latency for a given KS/CF.

Basically I want to inject a row in a node A and want to see how long it takes to get to node B (assuming proper RF is set).

I have already some network monitoring in our windows environment between my distributed nodes in place. But I still would like to get a handle on how a potential network and/or cassandra slowness affects inter-node latency. Maybe there is a tool/cmd that I'm not aware of? Tx.