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[GitHub] [spark] viirya opened a new pull request #26105: [SPARK-26570][SQL] Prevent OOM when transforming very many filestatus in InMemoryFileIndex.bulkListLeafFiles

viirya opened a new pull request #26105: [SPARK-26570][SQL] Prevent OOM when transforming very many filestatus in InMemoryFileIndex.bulkListLeafFiles
URL: https://github.com/apache/spark/pull/26105
 
 
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   ### What changes were proposed in this pull request?
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   This PR proposes to wrap the collected SerializableFileStatus with SoftReference, when collecting file statuses in InMemoryFileIndex.bulkListLeafFiles.
   
   Then later when we transform SerializableFileStatus back to Status, if there is memory pressure, traversed SerializableFileStatus can be candidates for GC.
   
   ### Why are the changes needed?
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   We get an array of (String, Seq[SerializableFileStatus]) when collecting file status in InMemoryFileIndex.bulkListLeafFiles. Then later we transform it back to sequence of (Path, Seq[FileStatus]).
   
   During the transforming, the items in the array are hold and can not be released by GC. Actually we double memory consumption here. When facing very many file status, this can be OOM.
   
   This change wraps the sequence of SerializableFileStatus with SoftReference in the array. So when we transform SerializableFileStatus back to Status, if there is memory pressure, traversed SerializableFileStatus can be candidates for GC.
   
   If SerializableFileStatus that is not traversed yet is cleared up by GC, we log necessary to users suggesting increasing driver memory. Then we re-list file status for the path.
   
   ### Does this PR introduce any user-facing change?
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   No
   
   ### How was this patch tested?
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   Unit test.

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