Files missing chunks can cause mapred runs to get stuck
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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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