[jira] [Commented] (SPARK-21056) InMemoryFileIndex.listLeafFiles should create at most one spark job when listing files in parallel

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

    [ https://issues.apache.org/jira/browse/SPARK-21056?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16045919#comment-16045919 ] 

Apache Spark commented on SPARK-21056:
--------------------------------------

User 'bbossy' has created a pull request for this issue:
https://github.com/apache/spark/pull/18269

> InMemoryFileIndex.listLeafFiles should create at most one spark job when listing files in parallel
> --------------------------------------------------------------------------------------------------
>
>                 Key: SPARK-21056
>                 URL: https://issues.apache.org/jira/browse/SPARK-21056
>             Project: Spark
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 2.1.1, 2.2.0
>            Reporter: Bertrand Bossy
>
> Given partitioned file relation (e.g. parquet):
> {code}
> root/a=../b=../c=..
> {code}
> InMemoryFileIndex.listLeafFiles runs numberOfPartitions(a) times numberOfPartitions(b) spark jobs sequentially to list leaf files, if both numberOfPartitions(a) and numberOfPartitions(b) are below {{spark.sql.sources.parallelPartitionDiscovery.threshold}} and numberOfPartitions(c) is above {{spark.sql.sources.parallelPartitionDiscovery.threshold}}
> Since the jobs are run sequentially, the overhead of the jobs dominates and the file listing operation can become significantly slower than listing the files from the driver.
> I propose that InMemoryFileIndex.listLeafFiles should launch at most one spark job for listing leaf files.



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