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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1296) Improve interface to FileSystem.getFileCacheHints
Date Wed, 25 Apr 2007 20:37:15 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1296?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12491762
] 

Hairong Kuang commented on HADOOP-1296:
---------------------------------------

I feel that we need either getStart() or getSize(). It seems that getSize() provides more
info than getStart() because we are able to figure out the end of last block. Another question,
does getFileHints still need the parameters "start" and "len"?

> Improve interface to FileSystem.getFileCacheHints
> -------------------------------------------------
>
>                 Key: HADOOP-1296
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1296
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: fs
>            Reporter: Owen O'Malley
>         Assigned To: dhruba borthakur
>
> The FileSystem interface provides a very limited interface for finding the location of
the data. The current method looks like:
> String[][] getFileCacheHints(Path file, long start, long len) throws IOException
> which returns a list of "block info" where the block info consists of a list host names.
Because the hints don't include the information about where the block boundaries are, map/reduce
is required to call the name node for each split. I'd propose that we fix the naming a bit
and make it:
> public class BlockInfo extends Writable {
>   public long getStart();
>   public String[] getHosts();
> }
> BlockInfo[] getFileHints(Path file, long start, long len) throws IOException;
> So that map/reduce can query about the entire file and get the locations in a single
call.

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