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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 23:36:15 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12493558
] 

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

I was just about to comment that open(...) is a convenience call, which combines 2 calls
DFSFileInfo getListing(src) and getBlockLocations(src, 0, length).
DFSFileInfo.fileLength if the only field that is widely used in current implementation.
So if folks can live without other fields like blockSize and blockReplication I am removing
open().



> 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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