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https://issues.apache.org/jira/browse/SPARK-35106?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Apache Spark reassigned SPARK-35106:
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Assignee: Apache Spark
> HadoopMapReduceCommitProtocol performs bad rename when dynamic partition
> overwrite is used
> ------------------------------------------------------------------------------------------
>
> Key: SPARK-35106
> URL: https://issues.apache.org/jira/browse/SPARK-35106
> Project: Spark
> Issue Type: Bug
> Components: Input/Output, Spark Core
> Affects Versions: 3.1.1
> Reporter: Erik Krogen
> Assignee: Apache Spark
> Priority: Major
>
> Recently when evaluating the code in
> {{HadoopMapReduceCommitProtocol#commitJob}}, I found some bad codepath under
> the {{dynamicPartitionOverwrite == true}} scenario:
> {code:language=scala}
> # BLOCK 1
> if (dynamicPartitionOverwrite) {
> val absPartitionPaths = filesToMove.values.map(new
> Path(_).getParent).toSet
> logDebug(s"Clean up absolute partition directories for overwriting:
> $absPartitionPaths")
> absPartitionPaths.foreach(fs.delete(_, true))
> }
> # BLOCK 2
> for ((src, dst) <- filesToMove) {
> fs.rename(new Path(src), new Path(dst))
> }
> # BLOCK 3
> if (dynamicPartitionOverwrite) {
> val partitionPaths = allPartitionPaths.foldLeft(Set[String]())(_ ++ _)
> logDebug(s"Clean up default partition directories for overwriting:
> $partitionPaths")
> for (part <- partitionPaths) {
> val finalPartPath = new Path(path, part)
> if (!fs.delete(finalPartPath, true) &&
> !fs.exists(finalPartPath.getParent)) {
> // According to the official hadoop FileSystem API spec, delete
> op should assume
> // the destination is no longer present regardless of return
> value, thus we do not
> // need to double check if finalPartPath exists before rename.
> // Also in our case, based on the spec, delete returns false only
> when finalPartPath
> // does not exist. When this happens, we need to take action if
> parent of finalPartPath
> // also does not exist(e.g. the scenario described on
> SPARK-23815), because
> // FileSystem API spec on rename op says the rename
> dest(finalPartPath) must have
> // a parent that exists, otherwise we may get unexpected result
> on the rename.
> fs.mkdirs(finalPartPath.getParent)
> }
> fs.rename(new Path(stagingDir, part), finalPartPath)
> }
> }
> {code}
> Assuming {{dynamicPartitionOverwrite == true}}, we have the following
> sequence of events:
> # Block 1 deletes all parent directories of {{filesToMove.values}}
> # Block 2 attempts to rename all {{filesToMove.keys}} to
> {{filesToMove.values}}
> # Block 3 does directory-level renames to place files into their final
> locations
> All renames in Block 2 will always fail, since all parent directories of
> {{filesToMove.values}} were just deleted in Block 1. Under a normal HDFS
> scenario, the contract of {{fs.rename}} is to return {{false}} under such a
> failure scenario, as opposed to throwing an exception. There is a separate
> issue here that Block 2 should probably be checking for those {{false}}
> return values -- but this allows for {{dynamicPartitionOverwrite}} to "work",
> albeit with a bunch of failed renames in the middle. Really, we should only
> run Block 2 in the {{dynamicPartitionOverwrite == false}} case, and
> consolidate Blocks 1 and 3 to run in the {{true}} case.
> We discovered this issue when testing against a {{FileSystem}} implementation
> which was throwing an exception for this failed rename scenario instead of
> returning false, escalating the silent/ignored rename failures into actual
> failures.
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