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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-894) dfs client protocol should allow asking for parts of the block map
Date Thu, 03 May 2007 18:49:15 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12493453
] 

Konstantin Shvachko commented on HADOOP-894:
--------------------------------------------

Yes, I can change the prototype to public DFSFileInfo open(String src) as Dhruba proposes.
But then open() will always return 10 blocks, and if we decide to implement something that
will require
only one block or all blocks on open we will not be able to optimize that.
So there is a trade off here functionality/flexibility vs simplicity.
I vote for flexibility in the case.

> dfs client protocol should allow asking for parts of the block map
> ------------------------------------------------------------------
>
>                 Key: HADOOP-894
>                 URL: https://issues.apache.org/jira/browse/HADOOP-894
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: Owen O'Malley
>         Assigned To: Konstantin Shvachko
>             Fix For: 0.13.0
>
>         Attachments: partialBlockList.patch, partialBlockList2.patch
>
>
> I think that the HDFS client protocol should change like:
> /** The meta-data about a file that was opened. */
> class OpenFileInfo {
>   /** the info for the first block */
>   public LocatedBlockInfo getBlockInfo();
>   public long getBlockSize();
>   public long getLength();
> }
> interface ClientProtocol extends VersionedProtocol {
>   public OpenFileInfo open(String name) throws IOException;
>   /** get block info for any range of blocks */
>   public LocatedBlockInfo[] getBlockInfo(String name, int blockOffset, int blockLength)
throws IOException;
> }
> so that the client can decide how much block info to request and when. Currently, when
the file is opened or an error occurs, the entire block list is requested and sent.

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