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https://issues.apache.org/jira/browse/HIVE-13429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15240350#comment-15240350
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Shannon Ladymon commented on HIVE-13429:
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[~daijy], thanks for adding clarification about *hive.scratchdir.lock*. I've
tried to summarize it as follows:
"When true, holds a lock file in the scratch directory. If a Hive process dies
and accidentally leaves a dangling scratchdir behind, the
cleardanglingscratchdir tool will remove it.
When false, does not create a lock file and therefore the
cleardanglingscratchdir tool cannot remove any dangling scratch directories."
Does that sound clear?
I've added documentation on parameter on the wiki:
* [Configuration Properties - hive.scratchdir.lock |
https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-hive.scratchdir.lock]
Before I add documentation on the *cleardanglingscratchdir* tool to the wiki, I
wanted to check with you about how broadly scratch directories apply in Hive.
Lefty had suggested putting it in the section on [Setting up HiveServer2 |
https://cwiki.apache.org/confluence/display/Hive/Setting+Up+HiveServer2], but
neither of us were sure if this information belonged in a more general section.
Is this primarily something for HiveServer2 (and CLI), or does this work on
other areas of Hive as well?
> 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
> Labels: TODOC1.3, TODOC2.1
> Fix For: 1.3.0, 2.1.0
>
> Attachments: HIVE-13429.1.patch, HIVE-13429.2.patch,
> HIVE-13429.3.patch, HIVE-13429.4.patch, HIVE-13429.5.patch,
> HIVE-13429.branch-1.patch
>
>
> 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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