[jira] [Created] (SPARK-50417) Limit number of subdirectories that FallbackStorage creates per shuffle

["Enrico Minack (Jira)" <ji...@apache.org>]

Enrico Minack created SPARK-50417:
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             Summary: Limit number of subdirectories that FallbackStorage creates per shuffle
                 Key: SPARK-50417
                 URL: https://issues.apache.org/jira/browse/SPARK-50417
             Project: Spark
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 4.0.0
            Reporter: Enrico Minack


The {{FallbackStorage}} copies shuffle data during executor decommissioning to a distributed or cloud storage like S3 or HDFS. In https://github.com/apache/spark/pull/34762, a hash has been added to the path of a file in order to reduce the number of files per directory (prefix in S3 terms). This creates as many directories per shuffle as files are transferred, while each directory contains a single file.

While this might be useful for S3, it may pose challenges for other filesystems. A shuffle of 100,000 partitions creates 100,000 directories, each containing a single file. The number of directories should be configurable to be able to adjust this behavior for the specific filesystem used.



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