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https://issues.apache.org/jira/browse/HADOOP-894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12495111
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Doug Cutting commented on HADOOP-894:
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> start out with a reasonable default and introduce a configuration variable
> when it appears to be needed
Two other options:
1. Make it configurable but don't document it in hadoop-default.xml.
2. Make it configurable but document it as an "expert" parameter. (We should
really go through hadoop-default.xml and mark things that most folks should
leave alone as expert.)
> 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
> 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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