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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-35) Files missing chunks can cause mapred runs to get stuck
Date Mon, 13 Feb 2006 18:30:43 GMT
Files missing chunks can cause mapred runs to get stuck
-------------------------------------------------------

         Key: HADOOP-35
         URL: http://issues.apache.org/jira/browse/HADOOP-35
     Project: Hadoop
        Type: Bug
  Components: dfs  
 Environment: ~20 datanode DFS cluster
    Reporter: Bryan Pendleton


I've now several times run into a problem where a large run gets stalled as a result of a
missing data block. The latest was a stall in the Summer - ie, the data might've all been
there, but it was impossible to proceed because the CRC file was missing a block. It would
be nice to:

1) Have a "health check" running on a map reduce. If any data isn't available, emmit periodic
warnings, and maybe have a timeout for if the data never comes back. Such warnings *should*
specify which file(s) are affected by the missing blocks.
2) Have a utility, possible part of the existing dfs utility, which can check for dfs files
with unlocatable blocks. Possibly, even show a 'health' of a file - ie, what percentage of
its blocks are currently at the desired replication level. Currently, there's no way that
I know of to find out if a file in DFS is going to be unreadable.

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