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https://issues.apache.org/jira/browse/HADOOP-894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12493580
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Sameer Paranjpye commented on HADOOP-894:
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I don't think we should remove open() just yet.
Long term it would be nice to have the POSIX semantics of a files blocks not
being removed while it is held open by a client even though the namespace entry
for the file is removed. In this situation, a client calling open() on a file
sets the expectation that it will need the files data until it either calls
close() or loses it's lease. We'd need the open() call to track open files. I
don't think getBlockLocations() alone is sufficient, it is ok to call
getBlockLocations() in order to get placement information for scheduling
without opening the file.
> 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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