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https://issues.apache.org/jira/browse/HBASE-17434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15814879#comment-15814879
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Duo Zhang commented on HBASE-17434:
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And have you heared about the DCL problem in java? After java 1.5, the problem
can be solved by adding volatile.
https://en.wikipedia.org/wiki/Double-checked_locking#Usage_in_Java
And I think the same thing could happen here. If you do not declare
readOnlyCopy as volatile, the assign could happen before the initialization of
the LinkedList. And the reader thread may get a uninitilaized LinkedList and
cause strange problems.
Thanks.
> New Synchronization Scheme for Compaction Pipeline
> --------------------------------------------------
>
> Key: HBASE-17434
> URL: https://issues.apache.org/jira/browse/HBASE-17434
> Project: HBase
> Issue Type: Bug
> Reporter: Eshcar Hillel
> Assignee: Eshcar Hillel
> Attachments: HBASE-17434-V01.patch, HBASE-17434-V02.patch,
> HBASE-17434-V03.patch, HBASE-17434-V04.patch, HBASE-17434.master.001.patch
>
>
> A new copyOnWrite synchronization scheme is introduced for the compaction
> pipeline.
> The new scheme is better since it removes the lock from getSegments() which
> is invoked in every get and scan operation, and it reduces the number of
> LinkedList objects that are created at runtime, thus can reduce GC (not by
> much, but still...).
> In addition, it fixes the method getTailSize() in compaction pipeline. This
> method creates a MemstoreSize object which comprises the data size and the
> overhead size of the segment and needs to be atomic.
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