[infinispan-issues] [JBoss JIRA] (ISPN-2067) The ConsistentHash implementation on the hotrod client is very inefficient

[Mircea Markus (JIRA)]

Mircea Markus created ISPN-2067:
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             Summary: The ConsistentHash implementation on the hotrod client is very inefficient
                 Key: ISPN-2067
                 URL: https://issues.jboss.org/browse/ISPN-2067
             Project: Infinispan
          Issue Type: Feature Request
    Affects Versions: 5.1.4.FINAL
            Reporter: Mircea Markus
            Assignee: Mircea Markus
             Fix For: 5.1.5.FINAL, 5.2.0.ALPHA1


Profiler snapshots show that a large amount of time is spent in the {{org.infinispan.client.hotrod.impl.consistenthash.ConsistentHashV1#getServer}} method (about 13%).
The root cause of this is the fact that the size method invoked on an object returned by TreeMap.tail() is very expensive: TreeMap.tail() returns an instance of TreeMap.AscendingSubMap class for which the size method, in order to calculates the number of elements, iterates over the entire collection(O(n)). This is highly inefficient and not scalable especially since the number of virtual nodes was set to 50 by default, as not the size of the collection is quite high: e.g. 32 nodes with 50 virtual nodes each, size()'s iterates an average of ~750 elements.  

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