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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1578) First step towards data transter protocol compatibility: support DatanodeProtocol#getDataTransferProtocolVersion
Date Tue, 11 Jan 2011 18:17:45 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12980223#action_12980223
] 

Todd Lipcon commented on HDFS-1578:
-----------------------------------

It seems like this could hurt efficiency for random workloads - we now have an extra RPC round
trip (with associated connection setup and teardown) for every DN connection... what's the
caching plan, etc? Could we keep the version numbers associated with each DN as part of the
datanode descriptor on the NN, and stuff it in the LocatedBlocks objects?

> 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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