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https://issues.apache.org/jira/browse/CASSANDRA-13964?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16227530#comment-16227530
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Jason Brown commented on CASSANDRA-13964:
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lgtm, and thanks for confirming my python skills aren't complete garbage :D
> Tracing interferes with digest requests when using RandomPartitioner
> --------------------------------------------------------------------
>
> Key: CASSANDRA-13964
> URL: https://issues.apache.org/jira/browse/CASSANDRA-13964
> Project: Cassandra
> Issue Type: Bug
> Components: Local Write-Read Paths, Observability
> Reporter: Sam Tunnicliffe
> Assignee: Sam Tunnicliffe
>
> A {{ThreadLocal<MessageDigest>}} is used to generate the MD5 digest when a
> replica serves a read command and the {{isDigestQuery}} flag is set. The same
> threadlocal is also used by {{RandomPartitioner}} to decorate partition keys.
> So in a cluster with RP, if tracing is enabled the data digest is corrupted
> by the partitioner making tokens for the tracing mutations. This causes a
> digest mismatch on the coordinator, triggering a full data read on every read
> where CL > 1 (or speculative execution/read repair kick in).
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