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From Tyler Hobbs <>
Subject Re: CompletedTasks attribute exposed via JMX
Date Wed, 12 Oct 2011 02:18:29 GMT
The OpsCenter graph you're referring to basically does the following:

1. For each node, find out how much the WriteOperations attribute of the
StorageProxy increased during the last minute.
2. Sum these values to get a total for the cluster.
3. Divide by 60 to get an average number of WriteOperations per second for
the cluster.

On Tue, Oct 11, 2011 at 3:55 PM, aaron morton <>wrote:

> Its the number of mutations, a mutation is a collection of changes for a
> single row across one or more column families.
> Take a look at the nodetool cfstats, this is where I assume Ops Centre is
> getting it's data from.
> Cheers
> -----------------
> Aaron Morton
> Freelance Cassandra Developer
> @aaronmorton
> On 12/10/2011, at 3:44 AM, Alexandru Dan Sicoe wrote:
> Hello everyone,
>  I was trying to get some cluster wide statistics of the total insertions
> performed in my 3 node Cassandra 0.8.6 cluster. So I wrote a nice little
> program that gets the CompletedTasks attribute of
> org.apache.cassandra.db:type=Commitlog from every node, sums up the values
> and records them in a .csv every 10 sec or so. Everything works and I get my
> stats but later I found out that I am not really sure what this measure
> means. I think it is the individual column insertions performed! Am I
> correct?
>  In the meantime I installed the trial version of the DataStax Operations
> Center. The cluster wide dashboard, showing Writes performed as a function
> of time, gives me much smaller values of the rates, compared to the
> measurement I described before. The Datastax writes/sec are of the same
> order of magnitude as the batch writes I perform on the cluster. But somehow
> I cannot relate between this rate and the rate of my CompletedTasks
> measurement.
> How do people usually measure insertion rates for their custers ? Per
> batch, per single columns or is actual data rate more important to know?
> Cheers,
> Alexandru

Tyler Hobbs
Software Engineer, DataStax <>
Maintainer of the pycassa <> Cassandra
Python client library

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