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Posted to issues@spark.apache.org by "Wenchen Fan (Jira)" <ji...@apache.org> on 2021/05/19 07:48:00 UTC
[jira] [Resolved] (SPARK-35106) HadoopMapReduceCommitProtocol
performs bad rename when dynamic partition overwrite is used
[ https://issues.apache.org/jira/browse/SPARK-35106?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Wenchen Fan resolved SPARK-35106.
---------------------------------
Fix Version/s: 3.0.3
3.1.2
3.2.0
Resolution: Fixed
Issue resolved by pull request 32530
[https://github.com/apache/spark/pull/32530]
> 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: Erik Krogen
> Priority: Major
> Fix For: 3.2.0, 3.1.2, 3.0.3
>
>
> 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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