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https://issues.apache.org/jira/browse/CASSANDRA-5263?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14045015#comment-14045015
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sankalp kohli commented on CASSANDRA-5263:
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Right. What I was proposing what that if we take the cardinality of the whole 
sstable, we will get a sense of overlapping. You are right, it won't be 
accurate. 
So not sure whether it is a good idea to use it. 

> Increase merkle tree depth as needed
> ------------------------------------
>
>                 Key: CASSANDRA-5263
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5263
>             Project: Cassandra
>          Issue Type: Improvement
>    Affects Versions: 1.1.9
>            Reporter: Ahmed Bashir
>            Assignee: Yuki Morishita
>             Fix For: 2.1.1
>
>         Attachments: 5263-2.1-v1.txt
>
>
> Currently, the maximum depth allowed for Merkle trees is hardcoded as 15.  
> This value should be configurable, just like phi_convict_treshold and other 
> properties.
> Given a cluster with nodes responsible for a large number of row keys, Merkle 
> tree comparisons can result in a large amount of unnecessary row keys being 
> streamed.
> Empirical testing indicates that reasonable changes to this depth (18, 20, 
> etc) don't affect the Merkle tree generation and differencing timings all 
> that much, and they can significantly reduce the amount of data being 
> streamed during repair. 



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