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From "Owen O'Malley (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1296) Improve interface to FileSystem.getFileCacheHints
Date Thu, 26 Apr 2007 07:45:15 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1296?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12491903
] 

Owen O'Malley commented on HADOOP-1296:
---------------------------------------

It shouldn't be 100's of thousands of records, because this is per a file. In the worst case
(100TB table in 1000 fragments with 128MB blocks), it will be 750 blocks or so. 

Furthermore, the proposed interface lets you ask about a subrange of the file, if it is more
that you want all at once.

> 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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