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https://issues.apache.org/jira/browse/SPARK-19501?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Marcelo Vanzin resolved SPARK-19501.
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Resolution: Fixed
Assignee: Jong Wook Kim
Fix Version/s: 2.2.0
2.1.1
2.0.3
> Slow checking if there are many spark.yarn.jars, which are already on HDFS
> --------------------------------------------------------------------------
>
> Key: SPARK-19501
> URL: https://issues.apache.org/jira/browse/SPARK-19501
> Project: Spark
> Issue Type: Improvement
> Components: YARN
> Affects Versions: 2.0.0, 2.0.1, 2.1.0
> Reporter: Jong Wook Kim
> Assignee: Jong Wook Kim
> Priority: Minor
> Fix For: 2.0.3, 2.1.1, 2.2.0
>
>
> Hi, this is my first Spark issue submission and please excuse any
> inconsistencies.
> I am experiencing a slower application startup time when I specify many files
> as {{spark.yarn.jars}}, by setting it as all JARs in an HDFS folder, such as
> {{hdfs://namenode/user/spark/lib/*.jar}}.
> Since the JAR files are already on the same HDFS that YARN is running, the
> application should be very fast to startup. However, the delay is significant
> especially when {{spark-submit}} is running from a non-local network, because
> {{spark-yarn}} accesses the individual JAR files via HDFS, adding hundreds of
> RTT before the application is ready. The official spark distribution with
> Hadoop 2.7 has more than 200 jars, and >100 even if we exclude Hadoop and its
> dependencies.
> There are currently two HDFS RPC calls for each file, once at
> {{ClientDistributedCacheManager.addResource}} calling {{fs.getFileStatus}},
> and another at {{yarn.Client.copyFileToRemote}} calling {{fc.resolvePath}}. I
> suppose that both are unnecessary, since we [already retrieved all
> FileStatuses, and that those are not
> symlinks|https://github.com/apache/spark/blob/v2.1.0/yarn/src/main/scala/org/apache/spark/deploy/yarn/Client.scala#L531].
> To fix this, I suppose that we can modify {{addResource}} to use its
> {{statCache}} variable before making an HDFS RPC and populate {{statCache}}
> appropriately before calling {{addResource}}. Also, an optional boolean
> parameter of {{copyFileToRemote}} can be added to skip the symlink check.
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