Daniel Dai created HIVE-13429:
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Summary: Tool to remove dangling scratch dir
Key: HIVE-13429
URL: https://issues.apache.org/jira/browse/HIVE-13429
Project: Hive
Issue Type: Improvement
Reporter: Daniel Dai
Assignee: Daniel Dai
We have seen in some cases, user will leave the scratch dir behind, and
eventually eat out hdfs storage. This could happen when vm restarts and leave
no chance for Hive to run shutdown hook. This is applicable for both HiveCli
and HiveServer2. Here we provide an external tool to clear dead scratch dir as
needed.
We need a way to identify which scratch dir is in use. We will rely on HDFS
write lock for that. Here is how HDFS write lock works:
1. A HDFS client open HDFS file for write and only close at the time of shutdown
2. Cleanup process can try to open HDFS file for write. If the client holding
this file is still running, we will get exception. Otherwise, we know the
client is dead
3. If the HDFS client dies without closing the HDFS file, NN will reclaim the
lease after 10 min, ie, the HDFS file hold by the dead client is writable again
after 10 min
So here is how we remove dangling scratch directory in Hive:
1. HiveCli/HiveServer2 opens a well-named lock file in scratch directory and
only close it when we about to drop scratch directory
2. A command line tool cleardanglingscratchdir will check every scratch
directory and try open the lock file for write. If it does not get exception,
meaning the owner is dead and we can safely remove the scratch directory
3. The 10 min window means it is possible a HiveCli/HiveServer2 is dead but we
still cannot reclaim the scratch directory for another 10 min. But this should
be tolerable
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