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https://issues.apache.org/jira/browse/HDFS-1578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12980242#action_12980242
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Hairong Kuang commented on HDFS-1578:
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Our use case of this is to support across cluster communications. We assume
that every datanode runs the same data transfer protocol in a cluster but two
clusters may run a slight different data transfer protocol versions. So the
client can fetch the version before any I/O starts. This is done once per
client not for every DN commection.
> First step towards data transter protocol compatibility: support
> DatanodeProtocol#getDataTransferProtocolVersion
> ----------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-1578
> URL: https://issues.apache.org/jira/browse/HDFS-1578
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Hairong Kuang
> Assignee: Hairong Kuang
> Fix For: 0.23.0
>
>
> HADOOP-6904 allows us to handle RPC changes in a compatible way. However, we
> have one more protocol to take care of, the data transfer protocol, which a
> dfs client uses to read data from or write data to a datanode.
>
> My proposal is to add a new RPC getDataTransferVersion to DatanodeProtocol
> that returns the data transfer protocol version running on the datanode. A
> dfs client gets the datanode's version number before it reads from/writes to
> a datanode. With this, the dfs client could behave differently according to
> datanode's data transfer version. This provides a base for us to make data
> transfer protocol changes in a compatible way.
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