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https://issues.apache.org/jira/browse/HADOOP-5146?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Devaraj Das updated HADOOP-5146:
--------------------------------
Attachment: 5146.patch
After some analysis, found the cause of the race condition:
1) Assume a fresh hdfs cluster with no files. Run a job (foo) that generates a
file in the hdfs called partition.lst
2) Run a job (bar) that uses the file foo generated. On a given node, one task
localizes partition.lst in the dist cache and other tasks simply use this
3) bar job finishes successfully without any task failures....
4) Now run foo again. This will regenerate the file partition.lst at the same
location.
5) Run bar again. On a given node that was used by the previous bar job, a task
t1 from the new bar job will still find the partition.lst in the cache in
ifExists() check. Context now switches to another taskrunner thread, say t2 of
the new bar job.
6) t2 also finds that ifExists() returns true but when it does getLocalCache,
it finds the file to be stale (since the file got regenerated in the foo job
again) and deletes it in DistributedCache.localizeCache. Context now switches
back to t1.
7) t1 does getLocalPathToRead and doesn't find the file... For t1, this is a
situation where ifExists() returns true, but getLocalPathToRead returns false
for the same path. This is the race condition..
The attached patch removes the call to ifExists/getLocalPathToRead in the
TaskRunner thread during the cache localization. It always does
getLocalPathForWrite. In the case where the file is already localized, the path
returned by getLocalPathForWrite will not be used and instead getLocalCache
will return the already localized path.
> LocalDirAllocator misses files on the local filesystem
> ------------------------------------------------------
>
> Key: HADOOP-5146
> URL: https://issues.apache.org/jira/browse/HADOOP-5146
> Project: Hadoop Core
> Issue Type: Bug
> Affects Versions: 0.20.0
> Reporter: Arun C Murthy
> Assignee: Devaraj Das
> Priority: Blocker
> Fix For: 0.20.0
>
> Attachments: 5146.patch, 5146.patch, 5146_20090204job.output.txt,
> localdirallocator.patch, localdirallocator.patch
>
>
> For some reason the LocalDirAllocator.getLocaPathToRead doesn't find files
> which are present, extra logging shows:
> {noformat}
> 2009-01-30 06:43:32,312 INFO
> org.apache.hadoop.fs.LocalDirAllocator$AllocatorPerContext: in ifExists,
> /grid/2/arunc/mapred-local/taskTracker/archive/xxx.yyy.com/tera/in/_partition.lst
> exists
> 2009-01-30 06:43:32,389 WARN
> org.apache.hadoop.fs.LocalDirAllocator$AllocatorPerContext: in
> getLocalPathToRead, taskTracker/archive/xxx.yyy.com/tera/in/_partition.lst
> doesn't exist
> 2009-01-30 06:43:32,390 WARN org.apache.hadoop.mapred.TaskRunner:
> attempt_200901300512_0007_m_000055_0 Child Error
> org.apache.hadoop.util.DiskChecker$DiskErrorException: Could not find
> taskTracker/archive/xx.yyy.com/tera/in/_partition.lst in any of the
> configured local directories
> at
> org.apache.hadoop.fs.LocalDirAllocator$AllocatorPerContext.getLocalPathToRead(LocalDirAllocator.java:388)
> at
> org.apache.hadoop.fs.LocalDirAllocator.getLocalPathToRead(LocalDirAllocator.java:138)
> at org.apache.hadoop.mapred.TaskRunner.run(TaskRunner.java:172)
> {noformat}
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