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https://issues.apache.org/jira/browse/HDFS-10636?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15486024#comment-15486024
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Virajith Jalaparti commented on HDFS-10636:
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Hi [~eddyxu],
That is a very valid concern. Our solution is to have a {{ProvidedReplica}}
class which inherits {{ReplicaInfo}}, and then have
{{ProvidedFinalizedReplica}} inherit {{ProvidedReplica}}. Not only this, we
will need to have a hierarchy for {{ProvidedReplica}} that mirrors the
hierarchy for {{LocalReplica}} in the patch. This is somewhat forced on us as
different classes are used to implicitly implement the replica state machine
(for example, {{ReplicaInfo::getBytesOnDisk()}} must resolve correctly in
{{FsDatasetImpl}}). Thus, we will also need to have
{{ProvidedReplicaInPipeline}}, {{ProvidedReplicaUnderRecovery}} and others
which inherit {{ProvidedReplica}}.
One way to avoid implementing such shadow classes for {{ProvidedReplica}} would
be to explicitly implement a state machine for the replicas. This would be a
much more disruptive change, with significant amount of new code and changes
required to several parts of {{FsDatasetImpl}}, and {{FsVolumeImpl}}. The
current patch keeps most of the code paths intact with relatively minor changes
to the APIs of {{ReplicaInfo}}.
> Modify ReplicaInfo to remove the assumption that replica metadata and data
> are stored in java.io.File.
> ------------------------------------------------------------------------------------------------------
>
> Key: HDFS-10636
> URL: https://issues.apache.org/jira/browse/HDFS-10636
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, fs
> Reporter: Virajith Jalaparti
> Assignee: Virajith Jalaparti
> Attachments: HDFS-10636.001.patch, HDFS-10636.002.patch,
> HDFS-10636.003.patch, HDFS-10636.004.patch, HDFS-10636.005.patch,
> HDFS-10636.006.patch, HDFS-10636.007.patch, HDFS-10636.008.patch,
> HDFS-10636.009.patch, HDFS-10636.010.patch
>
>
> Replace java.io.File related APIs from {{ReplicaInfo}}, and enable the
> definition of new {{ReplicaInfo}} sub-classes whose metadata and data can be
> present on external storages (HDFS-9806).
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