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https://issues.apache.org/jira/browse/MAPREDUCE-6685?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ray Chiang reopened MAPREDUCE-6685:
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> LocalDistributedCacheManager can have overlapping filenames
> -----------------------------------------------------------
>
> Key: MAPREDUCE-6685
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6685
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Affects Versions: 3.0.0-alpha1
> Reporter: Ray Chiang
> Assignee: Ray Chiang
> Attachments: MAPREDUCE-6685.001.patch, MAPREDUCE-6685.002.patch
>
>
> LocalDistributedCacheManager has this setup:
> bq. AtomicLong uniqueNumberGenerator = new
> AtomicLong(System.currentTimeMillis());
> to create this temporary filename:
> bq. new FSDownload(localFSFileContext, ugi, conf, new Path(destPath,
> Long.toString(uniqueNumberGenerator.incrementAndGet())), resource);
> when using LocalJobRunner. When two or more start on the same machine, then
> it's possible to end up having the same timestamp or a large enough overlap
> that two successive timestamps may not be sufficiently far apart.
> Given the assumptions:
> 1) Assume timestamp is the same. Then the most common starting random seed
> will be the same.
> 2) Process ID will very likely be unique, but will likely be close in value.
> 3) Thread ID is not guaranteed to be unique.
> A unique ID based on PID as a seed (in addition to the timestamp) should be a
> better unique identifier for temporary filenames.
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