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https://issues.apache.org/jira/browse/CASSANDRA-16721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17401177#comment-17401177
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Sam Tunnicliffe commented on CASSANDRA-16721:
---------------------------------------------
Your approach is a great improvement, makes a lot more sense for
{{ReadExecutionController}} to handle {{RepairedDataInfo}}. The only
non-obvious thing I noticed is that the sub-controllers for index reads should
probably not inherit the tracking flag, just always make it false. It should be
safe and not inefficient either way, but it just doesn't make sense for a read
of the index table to be set to track.
> Repaired data tracking on a read coordinator is susceptible to races between
> local and remote requests
> ------------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-16721
> URL: https://issues.apache.org/jira/browse/CASSANDRA-16721
> Project: Cassandra
> Issue Type: Bug
> Components: Consistency/Coordination
> Reporter: Sam Tunnicliffe
> Assignee: Caleb Rackliffe
> Priority: Normal
> Fix For: 4.0.x
>
>
> At read time on a coordinator which is also a replica, the local and remote
> reads can race such that the remote responses are received while the local
> read is executing. If the remote responses are mismatching, triggering a
> {{DigestMismatchException}} and subsequent round of full data reads and read
> repair, the local runnable may find the {{isTrackingRepairedStatus}} flag
> flipped mid-execution. If this happens after a certain point in execution,
> it would mean
> that the RepairedDataInfo instance in use is the singleton null object
> {{RepairedDataInfo.NULL_REPAIRED_DATA_INFO}}. If this happens, it can lead to
> an NPE when calling {{RepairedDataInfo::extend}} when the local results are
> iterated.
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