[jira] [Reopened] (CASSANDRA-5972) Reduce the amount of data to be transferred during repair

["Sylvain Lebresne (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-5972?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sylvain Lebresne reopened CASSANDRA-5972:
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You're right, I've read your suggestion a bit too quickly. If we do update the merkle trees after each pair of synchronization, we can indeed save some more transfer. Reopening since I was too quick at calling it a duplicate.
                
> Reduce the amount of data to be transferred during repair
> ---------------------------------------------------------
>
>                 Key: CASSANDRA-5972
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5972
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jacek Lewandowski
>            Priority: Minor
>
> Currently, when a validator finds a token range different in n replicas, data streams are initiated simultaneously between each possible pair of these n nodes, in both directions. It yields n*(n-1) data stream in total. 
> It can be done in a sequence - Replica[1] -> R[2], R[2] -> R[3], ... , R[n-1] -> R[n]. After this process, the data in R[n] are up to date. Then, we continue: R[n] -> R[1], R[1] -> R[2], ... , R[n-2] -> R[n-1]. The active repair is done after 2*(n-1) data transfers performed sequentially in 2*(n-1) steps.

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