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https://issues.apache.org/jira/browse/SPARK-25062?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16641152#comment-16641152
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Peter Toth commented on SPARK-25062:
------------------------------------
Thanks [~dongjoon]. :)
> Clean up BlockLocations in FileStatus objects
> ---------------------------------------------
>
> Key: SPARK-25062
> URL: https://issues.apache.org/jira/browse/SPARK-25062
> Project: Spark
> Issue Type: Improvement
> Components: Spark Core
> Affects Versions: 2.2.2
> Reporter: andrzej.stankev...@gmail.com
> Assignee: Peter Toth
> Priority: Major
> Fix For: 3.0.0
>
> Attachments: petertoth.png
>
>
> When Spark lists collection of files it does it on a driver or creates tasks
> to list files depending on number of files. here
> [https://github.com/apache/spark/blob/branch-2.2/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/InMemoryFileIndex.scala#L170]
> If spark creates tasks to list files each task creates one FileStatus object
> per file. Before sending FileStatus to a driver Spark converts FileStatus to
> SerializableFileStatus. On driver side Spark turns SerializableFileStatus
> back to FileStatus and it also creates BlockLocation object for each
> FileStatus using
>
> {code:java}
> new BlockLocation(loc.names, loc.hosts, loc.offset, loc.length)
> {code}
>
> After deserialization on a driver side BlockLocation doesn't have a lot of
> information that original HDFSBlockLocation had.
>
> If Spark does listing on a driver side FileStatus object has
> HSDFBlockLocation objects and they have a lot of info that Spark doesn't use.
> Because of this FileStatus objects takes more memory than if it would created
> on executor side.
>
> Later Spark puts all this objects into _SharedInMemoryCache_ and that cache
> takes 2.2x more memory if files were listed on driver side than if they were
> listed on executor side.
>
> In our case _SharedInMemoryCache_ takes 125M when we do scan on executors
> and 270M when we do it on a driver. It is for about 19000 files.
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