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From "Joe Pallas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10636) Modify ReplicaInfo to remove the assumption that replica metadata and data are stored in java.io.File.
Date Wed, 24 Aug 2016 00:12:21 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10636?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15433904#comment-15433904
] 

Joe Pallas commented on HDFS-10636:
-----------------------------------

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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