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https://issues.apache.org/jira/browse/MAPREDUCE-5278?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Xi Fang updated MAPREDUCE-5278:
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Description:
Today, the JobTracker staging dir ("mapreduce.jobtracker.staging.root.dir) is
set to point to HDFS, even though other file systems (e.g. Amazon S3 file
system and Windows ASV file system) are the default file systems. For ASV, this
config was chosen and there are a few reasons why:
1. To prevent leak of the storage account creds to the user's storage account;
2. It uses HDFS for the transient job files what is good for two reasons – a)
it does not flood the user's storage account with irrelevant data/files b) it
leverages HDFS locality for small files
However, this approach conflicts with how distributed cache caching works,
completely negating the feature's functionality.
When files are added to the distributed cache (thru files/achieves/libjars
hadoop generic options), they are copied to the job tracker staging dir only if
they reside on a file system different that the jobtracker's. Later on, this
path is used as a "key" to cache the files locally on the tasktracker's
machine, and avoid localization (download/unzip) of the distributed cache files
if they are already localized.
In this configuration the caching is completely disabled and we always end up
copying dist cache files to the job tracker's staging dir first and localizing
them on the task tracker machine second.
This is especially not good for Oozie scenarios as Oozie uses dist cache to
populate Hive/Pig jars throughout the cluster.
was:
Today, we set the JobTracker staging dir
("mapreduce.jobtracker.staging.root.dir) to point to HDFS even though ASV is
the default file system. There are a few reason why this config was chosen:
1. To prevent leak of the storage account creds to the user's storage account
(IOW, keep job.xml in the cluster).
2. It uses HDFS for the transient job files what is good for two reasons – a)
it does not flood the user's storage account with irrelevant data/files b) it
leverages HDFS locality for small files
However, this approach conflicts with how distributed cache caching works,
completely negating the feature's functionality.
When files are added to the distributed cache (thru files/achieves/libjars
hadoop generic options), they are copied to the job tracker staging dir only if
they reside on a file system different that the jobtracker's. Later on, this
path is used as a "key" to cache the files locally on the tasktracker's
machine, and avoid localization (download/unzip) of the distributed cache files
if they are already localized.
In our configuration the caching is completely disabled and we always end up
copying dist cache files to the JT staging dir first and localizing them on the
tasktracker machine second.
This is especially not good for Oozie scenarios as Oozie uses dist cache to
populate Hive/Pig jars throughout the cluster.
Easy workaround is to config mapreduce.jobtracker.staging.root.dir in
mapred-site.xml to be on the default FS.
> Perf: Distributed cache is broken when JT staging dir is not on the default FS
> ------------------------------------------------------------------------------
>
> Key: MAPREDUCE-5278
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5278
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: distributed-cache
> Affects Versions: 1-win
> Environment: Windows
> Reporter: Xi Fang
> Assignee: Xi Fang
>
> Today, the JobTracker staging dir ("mapreduce.jobtracker.staging.root.dir) is
> set to point to HDFS, even though other file systems (e.g. Amazon S3 file
> system and Windows ASV file system) are the default file systems. For ASV,
> this config was chosen and there are a few reasons why:
> 1. To prevent leak of the storage account creds to the user's storage
> account;
> 2. It uses HDFS for the transient job files what is good for two reasons – a)
> it does not flood the user's storage account with irrelevant data/files b) it
> leverages HDFS locality for small files
> However, this approach conflicts with how distributed cache caching works,
> completely negating the feature's functionality.
> When files are added to the distributed cache (thru files/achieves/libjars
> hadoop generic options), they are copied to the job tracker staging dir only
> if they reside on a file system different that the jobtracker's. Later on,
> this path is used as a "key" to cache the files locally on the tasktracker's
> machine, and avoid localization (download/unzip) of the distributed cache
> files if they are already localized.
> In this configuration the caching is completely disabled and we always end up
> copying dist cache files to the job tracker's staging dir first and
> localizing them on the task tracker machine second.
> This is especially not good for Oozie scenarios as Oozie uses dist cache to
> populate Hive/Pig jars throughout the cluster.
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