[jira] [Assigned] (SPARK-19501) Slow checking if there are many spark.yarn.jars, which are already on HDFS

["Apache Spark (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-19501?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Apache Spark reassigned SPARK-19501:
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    Assignee: Apache Spark

> 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: Apache Spark
>            Priority: Minor
>
> 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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