[jira] [Resolved] (CASSANDRA-4598) describeOwnership() in Murmur3Partitioner.java doesn't work for close tokens

["Yuki Morishita (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-4598?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Yuki Morishita resolved CASSANDRA-4598.
---------------------------------------

       Resolution: Fixed
    Fix Version/s: 1.2.0 rc2

We fixed desribeOwnership bug in CASSANDRA-5076, and the above issue was resolved also. Closing this as 'Fixed'.
                
> describeOwnership() in Murmur3Partitioner.java doesn't work for close tokens
> ----------------------------------------------------------------------------
>
>                 Key: CASSANDRA-4598
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4598
>             Project: Cassandra
>          Issue Type: Bug
>    Affects Versions: 1.2.0
>            Reporter: Julien Lambert
>            Priority: Minor
>             Fix For: 1.2.0 rc2
>
>
> On a 2 node-cluster, if the two tokens are close enough, the ownership information displayed will be 0.00% for each, instead of ~0% for one and ~100% for the other. The number of replicas displayed is then 0, even if you have more.
> Reproduce:
> - Create a 2-node cluster, using Murmur3Partitioner
> - Move the tokens to two consecutive values
> - Display ring with nodetool
> Problem:
> This line causing this problem is in {{describeOwnership()}} of {{Murmur3Partitioner.java}} (lines 117 and 123):
> {{float age = ((ti - tim1 + ri) % ri) / ri;}}
> If {{ti - tim1}} (the difference of the two consecutive tokens) is too small, then the precision of the float isn't enough to represent the exact numbers (because {{ri}}, the total range of the ring, is a very big number). 
> For example, {{(float) (ri + 1) = (float) (ri - 1) = (float) ri = 9.223372E18}}, so that {{((ri+1)%ri)/ri = ((ri-1)%ri)/ri = (ri%ri)/ri = 0}}. Whereas with a correct precision, the exact value for {{(ri-1)%ri}} should be {{ri-1}} and {{(ri-1)/ri ~ 1.0 (100%)}} instead of 0%.
> Also, as the number of replica is determined by NodeCmd using the ownership percentages, it is wrong too.
> Solution:
> We might want to use BigInteger or BigDecimal somewhere?

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