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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-894) dfs client protocol should allow asking for parts of the block map
Date Fri, 11 May 2007 18:05:15 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-894?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12495111
] 

Doug Cutting commented on HADOOP-894:
-------------------------------------

> 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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