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https://issues.apache.org/jira/browse/CASSANDRA-15461?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17000054#comment-17000054
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Sam Tunnicliffe edited comment on CASSANDRA-15461 at 12/19/19 1:23 PM:
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The patch abstracts the digest generation, wrapping the underlying {{Hasher}} 
with a new {{Digest}} class. Specializations of {{Digest}} can incorporate 
logic depending on their specific usage; e.g. when generating a digest for 
repaired data tracking, don't include legacy counter shards. This also enables 
a lot of {{ByteBuffer}} duplication to be removed.

||branch||CI||
|[15461-4.0|https://github.com/beobal/cassandra/tree/15461-4.0]|[circle|https://circleci.com/gh/beobal/workflows/cassandra/tree/15461-4.0]|



was (Author: beobal):
||branch||CI||
|[15461-4.0|https://github.com/beobal/cassandra/tree/15461-4.0]|[circle|https://circleci.com/gh/beobal/workflows/cassandra/tree/15461-4.0]|


> Legacy counter shards can cause false positives in repaired data tracking
> -------------------------------------------------------------------------
>
>                 Key: CASSANDRA-15461
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15461
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Observability/Metrics
>            Reporter: Sam Tunnicliffe
>            Assignee: Sam Tunnicliffe
>            Priority: Normal
>             Fix For: 4.0-beta
>
>
> It is expected that the serialization of legacy (pre-2.1) counter cells may 
> differ across replicas due to the remote vs local designation of the shards. 
> This will cause the repaired data digests calculated at read time to differ 
> where certain legacy shards are encountered. This does not, however, indicate 
> corruption of the repaired dataset and there isn't any action that operators 
> can take in this scenario. Excluding counter cells which contain legacy 
> shards from the digest calculation will avoid false positives.



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