[jira] [Commented] (HDFS-8924) Add pluggable interface for reading replicas in DFSClient

["Colin Patrick McCabe (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-8924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14703916#comment-14703916 ] 

Colin Patrick McCabe commented on HDFS-8924:
--------------------------------------------

This patch adds a pluggable {{ReplicaAccessorBuilder}} class which can be used to create {{ReplicaAccessor}} objects.  Unlike {{BlockReader}}, {{ReplicaAccessor}} is a stable API which is decoupled from internal implementation details and non-public classes.  {{BlockReaderFactory}} will ask all of the configured {{ReplicaAccessorBuilder}} objects to create a new {{ReplicaAccessor}}.  If none are configured, or none can create one, we use the existing block reader code.  Otherwise, we create an {{ExternalBlockReader}} wrapping the {{ReplicaAccessor}}.  I also added a reserved {{DataTransferProtocol}} opcode (127) in {{Op.java}}.  This will ensure that anyone adding a custom opcode will not conflict with other new opcodes added upstream.

> Add pluggable interface for reading replicas in DFSClient
> ---------------------------------------------------------
>
>                 Key: HDFS-8924
>                 URL: https://issues.apache.org/jira/browse/HDFS-8924
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs-client
>    Affects Versions: 2.8.0
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>         Attachments: HDFS-8924.001.patch
>
>
> We should add a pluggable interface for reading replicas in the DFSClient.  This could be used to implement short-circuit reads on systems without file descriptors, or for other optimizations.



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