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https://issues.apache.org/jira/browse/CASSANDRA-13877?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16170009#comment-16170009
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Joshua McKenzie commented on CASSANDRA-13877:
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Those volatiles are only written from one thread context each so shouldn't be
an issue; single-producer multi-consumer.
bq. In rare cases we'll not be able to calculate CDC data size correctly
Could you clarify a theoretical scenario in which this would take place?
> Potential concurrency issue with CDC size calculation
> -----------------------------------------------------
>
> Key: CASSANDRA-13877
> URL: https://issues.apache.org/jira/browse/CASSANDRA-13877
> Project: Cassandra
> Issue Type: Bug
> Reporter: Simon Zhou
> Assignee: Simon Zhou
>
> We're backporting CDC feature and bug fixes to 3.0. There is potential
> visibility issue with two variables {{CDCSizeTracker.sizeInProgress}} and
> {{DirectorySizeCalculator.size}} . They're declared as volatile however there
> are cases that when assigning new values to them, the new values depend on
> the current value. For example:
> https://github.com/apache/cassandra/blob/e9da85723a8dd40872c4bca087a03b655bd2cacb/src/java/org/apache/cassandra/db/commitlog/CommitLogSegmentManagerCDC.java#L285
> https://github.com/apache/cassandra/blob/e9da85723a8dd40872c4bca087a03b655bd2cacb/src/java/org/apache/cassandra/db/commitlog/CommitLogSegmentManagerCDC.java#L297
> In rare cases we'll not be able to calculate CDC data size correctly. We
> should change these two variables back to AtomicLong, as the simplest fix.
> Java Concurrency In Practice section 3.1.3 explains well why we shouldn't use
> volatile in these two cases. I'll provide patch shortly.
> cc [~JoshuaMcKenzie] [~jay.zhuang]
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