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https://issues.apache.org/jira/browse/HDFS-8499?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14632095#comment-14632095
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Zhe Zhang commented on HDFS-8499:
---------------------------------
Thanks for the discussions Nicholas and Jing.
Basically, I think the long term solution to this multi-inheritance is to
eliminate {{BlockInfo}} subclassing altogether and using feature / op classes
instead, like {{INodeFile}} features. It is more explicit, clearer, and safer
than relying on {{instanceof}} and type casting. Moreover, it allows scaling to
more types of {{BlockInfo}}. For example, as mentioned above, in phase II of
erasure coding we will likely support contiguous + erasure coded blocks.
*If* we agree upon the long term solution, then *A* and *B*, as Nicholas
summarized, are both intermediate states. I chose option *A* primarily to
minimize change and keep trunk more stable. A secondary reason is to get rid of
duplicate code between the two UC classes. I started writing a patch to make UC
an Op class but found it much more change than contiguous / striped Op classes.
> Refactor BlockInfo class hierarchy with static helper class
> -----------------------------------------------------------
>
> Key: HDFS-8499
> URL: https://issues.apache.org/jira/browse/HDFS-8499
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Affects Versions: 2.7.0
> Reporter: Zhe Zhang
> Assignee: Zhe Zhang
> Fix For: 2.8.0
>
> Attachments: HDFS-8499.00.patch, HDFS-8499.01.patch,
> HDFS-8499.02.patch, HDFS-8499.03.patch, HDFS-8499.04.patch,
> HDFS-8499.05.patch, HDFS-8499.06.patch, HDFS-8499.07.patch,
> HDFS-8499.UCFeature.patch, HDFS-bistriped.patch
>
>
> In HDFS-7285 branch, the {{BlockInfoUnderConstruction}} interface provides a
> common abstraction for striped and contiguous UC blocks. This JIRA aims to
> merge it to trunk.
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