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https://issues.apache.org/jira/browse/CASSANDRA-5263?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13890422#comment-13890422
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Jonathan Ellis commented on CASSANDRA-5263:
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Why don't we just pick the depth that covers the appropriate number of
partitions/hashes? 2**16 = 64K, 2**17 = 128K, etc.
> Allow Merkle tree maximum depth to be configurable
> --------------------------------------------------
>
> Key: CASSANDRA-5263
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5263
> Project: Cassandra
> Issue Type: Improvement
> Components: Config
> Affects Versions: 1.1.9
> Reporter: Ahmed Bashir
> Assignee: Minh Do
>
> 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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