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https://issues.apache.org/jira/browse/CASSANDRA-6758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13910811#comment-13910811
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sankalp kohli commented on CASSANDRA-6758:
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If you are depending on extrapolated, you can see how many ranges did not match
during repair. This will give you a similar answer as this info is logged.
Also since, a tree range/leaf can have multiple rows, you can calculate that by
knowing the number of rows per instance and dividing by 32k leafs of Merkle
tree.
> Measure data consistency in the cluster
> ---------------------------------------
>
> Key: CASSANDRA-6758
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6758
> Project: Cassandra
> Issue Type: New Feature
> Reporter: Jimmy Mårdell
> Priority: Minor
>
> Running multi-DC Cassandra can be a challenge as the cluster easily tends to
> get out-of-sync. We have been thinking it would be nice to measure how out of
> sync a cluster is and expose those metrics somehow.
> One idea would be to just run the first half of the repair process and output
> the result of the differencer. If you use Random or the Murmur3 partitioner,
> it should be enough to calculate the merkle tree over a small subset of the
> ring as the result can be extrapolated.
> This could be exposed in nodetool. Either a separate command or perhaps a
> dry-run flag to repair?
> Not sure about the output format. I think it would be nice to have one value
> ("% consistent"?) within a DC, and also one value for every pair of DC's
> perhaps?
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