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https://issues.apache.org/jira/browse/HDFS-10636?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15433904#comment-15433904
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Joe Pallas commented on HDFS-10636:
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Possibly the only requirement to subclass {{FinalizedReplica}} today is that it
appears in the dataset SPI, so any alternative implementation has to use it.
The proposal removes that, so maybe there isn't a strong reason to have it be a
type (if I understand the distinction I think [~virajith] is making between
class as type and class as state). There are several places in the current
patch where {{FinalizedReplica}} becomes {{ReplicaInfo}}, and I think that's a
reasonable change.
The concern [~eddyxu] expressed above about states and types is valid, but, in
this case, I think the type system isn't really helping the programmer very
much. Existing code using {{FinalizedReplica}} is already frequently stuck
with only {{ReplicaInfo}} known at compile time, so a state check is needed
anyway, and using a cast to {{FinalizedReplica}} after the state check doesn't
add much.
> 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
>
>
> 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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