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https://issues.apache.org/jira/browse/HADOOP-894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12493447
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dhruba borthakur commented on HADOOP-894:
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One issue we discussed earlier: The ClientProtocol open method used to take a
path name. It was of the form:
public LocatedBlock[] open(String src)
This patch changes it to
public DFSFileInfo open(String src, long length)
The modified "open" API is not very intuitive because it is taking a "length"
parameter. If we want to keep the ClientProtocol elegant and simple, we might
want to remove the "length" parameter from call. The server is free to send
back as many block locations as it deems fit. Typically, the server will be
send one or two block locations.
> 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
>
>
> 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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