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https://issues.apache.org/jira/browse/HADOOP-18797?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17779784#comment-17779784
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ASF GitHub Bot commented on HADOOP-18797:
-----------------------------------------

shameersss1 commented on PR #6122:
URL: https://github.com/apache/hadoop/pull/6122#issuecomment-1780575205

   > looks good and I'm not going to review backports except for backporting 
issues.
   > 
   > which s3 region did you test against, and with what parameters?
   
   How was this patch tested?
   
       1. Ran S3A Unit Tests
   
       2. Ran S3A Integration test in us-west-1 region
   
   [INFO] Running 
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> Support Concurrent Writes With S3A Magic Committer
> --------------------------------------------------
>
>                 Key: HADOOP-18797
>                 URL: https://issues.apache.org/jira/browse/HADOOP-18797
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs/s3
>            Reporter: Emanuel Velzi
>            Assignee: Syed Shameerur Rahman
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 3.4.0
>
>
> There is a failure in the commit process when multiple jobs are writing to a 
> s3 directory *concurrently* using {*}magic committers{*}.
> This issue is closely related HADOOP-17318.
> When multiple Spark jobs write to the same S3A directory, they upload files 
> simultaneously using "__magic" as the base directory for staging. Inside this 
> directory, there are multiple "/job-some-uuid" directories, each representing 
> a concurrently running job.
> To fix some preoblems related to concunrrency a property was introduced in 
> the previous fix: "spark.hadoop.fs.s3a.committer.abort.pending.uploads". When 
> set to false, it ensures that during the cleanup stage, finalizing jobs do 
> not abort pending uploads from other jobs. So we see in logs this line: 
> {code:java}
> DEBUG [main] o.a.h.fs.s3a.commit.AbstractS3ACommitter (819): Not cleanup up 
> pending uploads to s3a ...{code}
> (from 
> [AbstractS3ACommitter.java#L952|https://github.com/apache/hadoop/blob/trunk/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/commit/AbstractS3ACommitter.java#L952])
> However, in the next step, the {*}"__magic" directory is recursively 
> deleted{*}:
> {code:java}
> INFO  [main] o.a.h.fs.s3a.commit.magic.MagicS3GuardCommitter (98): Deleting 
> magic directory s3a://my-bucket/my-table/__magic: duration 0:00.560s {code}
> (from [AbstractS3ACommitter.java#L1112 
> |https://github.com/apache/hadoop/blob/trunk/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/commit/AbstractS3ACommitter.java#L1112]and
>  
> [MagicS3GuardCommitter.java#L137)|https://github.com/apache/hadoop/blob/trunk/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/commit/magic/MagicS3GuardCommitter.java#L137)]
> This deletion operation *affects the second job* that is still running 
> because it loses pending uploads (i.e., ".pendingset" and ".pending" files).
> The consequences can range from an exception in the best case to a silent 
> loss of data in the worst case. The latter occurs when Job_1 deletes files 
> just before Job_2 executes "listPendingUploadsToCommit" to list ".pendingset" 
> files in the job attempt directory previous to complete the uploads with POST 
> requests.
> To resolve this issue, it's important {*}to ensure that only the prefix 
> associated with the job currently finalizing is cleaned{*}.
> Here's a possible solution:
> {code:java}
> /**
>  * Delete the magic directory.
>  */
> public void cleanupStagingDirs() {
>   final Path out = getOutputPath();
>  //Path path = magicSubdir(getOutputPath());
>   Path path = new Path(magicSubdir(out), formatJobDir(getUUID()));
>   try(DurationInfo ignored = new DurationInfo(LOG, true,
>       "Deleting magic directory %s", path)) {
>     Invoker.ignoreIOExceptions(LOG, "cleanup magic directory", 
> path.toString(),
>         () -> deleteWithWarning(getDestFS(), path, true));
>   }
> } {code}
>  
> The side effect of this issue is that the "__magic" directory is never 
> cleaned up. However, I believe this is a minor concern, even considering that 
> other folders such as "_SUCCESS" also persist after jobs end.



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