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From Wei Zhu <wz1...@yahoo.com>
Subject Re: read request distribution
Date Tue, 13 Nov 2012 20:43:00 GMT
I am new to Cassandra, and 1.1.6 is the only version I have tested. Not sure about the old
behavior, for 1.1.6, my observation is that for brand new cluster (with no CF created), it
shows Ownership from nodetool ring, the value is 100/<nodes>. As soon as one CF is
created, the column changes to Effective Ownership and the formula seems to be 100*<replication
factor>/<nodes> as Kirk mentioned. .Theoretically, different keyspace can have different
replication factor. Not sure how Effective Ownership is calculated in that cases. Just curious
anyone knows?

Thanks.
-Wei


________________________________
 From: Kirk True <kirk@mustardgrain.com>
To: user@cassandra.apache.org 
Sent: Monday, November 12, 2012 4:24 PM
Subject: Re: read request distribution
 

 
Somewhat recently the Ownership column was changed to Effective Ownership. 

 
Previously the formula was essentially 100/<nodes>. Now it's 100*<replication factor>/<nodes>.
So in previous releases of Cassandra it would be 100/12 = 8.33, now it would be closer to
25% (8.33*3 (assuming a replication factor of three)).

 
Kirk

 
On Mon, Nov 12, 2012, at 03:52 PM, Ananth Gundabattula wrote:

Hi all,
>
> 
>On an unrelated observation of the below readings, it looks like all the 3 nodes own 100%
of the data. This confuses me a bit. We have a 12 node cluster with RF=3 but the effective
ownership is shown as 8.33 % . 
>
> 
>So here is my question. How is the ownership calculated : Is Replica factor considered
in the ownership calculation ? ( If yes , then 8.33 % ownership of a cluster seems wrong to
me . If not 100% ownership for a node cluster seems wrong to me. Am I missing something in
the calculation? 
>
> 
>Regards,
>
>Ananth
>
> 
>On Fri, Nov 9, 2012 at 4:37 PM, Wei Zhu <wz1975@yahoo.com> wrote:
>
>Hi All,
>>
>>I am doing a benchmark on a Cassandra. I have a three node cluster with RF=3. I generated
6M rows with sequence  number from 1 to 6m, so the rows should be evenly distributed among
the three nodes disregarding the replicates. 
>>
>>I am doing a benchmark with read only requests, I generate read request for randomly
generated keys from 1 to 6M. Oddly, nodetool cfstats, reports that one node has only half
the requests as the other one and the third node sits in the middle. So the ratio is like
2:3:4. The node with the most read requests actually has the smallest latency and the one
with the least read requests reports the largest latency. The difference is pretty big, the
fastest is almost double the slowest.
>>
>>All three nodes have the exactly the same hardware and the data size on each node
are the same since the RF is three and all of them have the complete data. I am using Hector
as client and the random read request are in millions. I can't think of a reasonable explanation. 
Can someone please shed some lights?
>>
>> 
>>Thanks.
>>-Wei
>>
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