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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5263) Allow Merkle tree maximum depth to be configurable
Date Tue, 04 Feb 2014 06:04:11 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5263?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13890422#comment-13890422
] 

Jonathan Ellis commented on CASSANDRA-5263:
-------------------------------------------

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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