Julien Lambert created CASSANDRA-4598:
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Summary: 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
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.
Reproduce:
- Create a 2-node cluster, using Murmur3Partitioner
- Move the tokens to two consecutive values
- Display ring with nodetool
Problem:
This line is causing the problem 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.
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%.
Solution:
We might want to use BigDecimal instead of float?
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