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From Stephan P <steplmi4...@gmail.com>
Subject Re: Measure Latency
Date Wed, 25 May 2011 17:56:06 GMT
Thanks for the reply.

I agree about the eventual consistency feature but in "addition" I'm trying
to have an oversight if there is a slowness between nodes in a cluster
meaning sometimes "some" network slowness won't translate in CA slowness and
sometimes it will. I guess I'm looking for a process that tells me what the
actual travel time between CA Node A and B is.

Here is very simple way how the same is done with SQL Server replication
(sorry to wonder off into the RDBMS world):
I insert a single timestamp into a small table and let SQL server replicate
it to nodes. Upon arrival on each node the insert will automatically
generate a default timestamp value into the same table/row. Taking the diff
between original inserted (source) and default insert (target) timestamp I
know precisely how long it took to push that content along within SQL
Server.



On Tue, May 24, 2011 at 11:46 PM, Aaron Morton <aaron@thelastpickle.com>wrote:

> 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
> @aaronmortonhttp://www.thelastpickle.com
>
>
> On 25 May, 2011,at 03:11 PM, Stephan Pfammatter <steplmi4124@gmail.com>
> wrote:
>
> What’s the recommended way of measuring latency between nodes in a cluster?
>
>
> By that I’m 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.
>
>

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