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https://issues.apache.org/jira/browse/HADOOP-16721?focusedWorklogId=563113&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-563113
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ASF GitHub Bot logged work on HADOOP-16721:
-------------------------------------------
Author: ASF GitHub Bot
Created on: 09/Mar/21 14:57
Start Date: 09/Mar/21 14:57
Worklog Time Spent: 10m
Work Description: steveloughran commented on a change in pull request
#2742:
URL: https://github.com/apache/hadoop/pull/2742#discussion_r590442351
##########
File path:
hadoop-tools/hadoop-aws/src/site/markdown/tools/hadoop-aws/troubleshooting_s3a.md
##########
@@ -1126,6 +1126,26 @@ We also recommend using applications/application
options which do not rename files when committing work or when copying data
to S3, but instead write directly to the final destination.
+## Rename not behaving as "expected"
+
+S3 is not a filesystem. The S3A connector mimics rename by
+
+* HEAD then LIST of source path
+* HEAD then LIST of destination path
+* File-by-file copy of source objects to destination.
+ Parallelized, with page listings of directory objects and issuing of DELETE
requests.
+* Post-delete recreation of destination parent directory marker, if needed.
Review comment:
oops. fixed
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Issue Time Tracking
-------------------
Worklog Id: (was: 563113)
Time Spent: 1h 50m (was: 1h 40m)
> Improve S3A rename resilience
> -----------------------------
>
> Key: HADOOP-16721
> URL: https://issues.apache.org/jira/browse/HADOOP-16721
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 3.2.0
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Blocker
> Labels: pull-request-available
> Time Spent: 1h 50m
> Remaining Estimate: 0h
>
> h3. race condition in delete/rename overlap
> If you have multiple threads on a system doing rename operations, then one
> thread doing a delete(dest/subdir) may delete the last file under a subdir,
> and, before its listed and recreated any parent dir marker -other threads may
> conclude there's an empty dest dir and fail.
> This is most likely on an overloaded system with many threads executing
> rename operations, as with parallel copying taking place there are many
> threads to schedule and https connections to pool.
> h3. failure reporting
> the classic \{[rename(source, dest)}} operation returns \{{false}} on certain
> failures, which, while somewhat consistent with the posix APIs, turns out to
> be useless for identifying the cause of problems. Applications tend to have
> code which goes
> {code}
> if (!fs.rename(src, dest)) throw new IOException("rename failed");
> {code}
> While ultimately the rename/3 call needs to be made public (HADOOP-11452) it
> would then need a adoption across applications. We can do this in the hadoop
> modules, but for Hive, Spark etc it will take along time.
> Proposed: a switch to tell S3A to stop downgrading certain failures (source
> is dir, dest is file, src==dest, etc) into "false". This can be turned on
> when trying to diagnose why things like Hive are failing.
> Production code: trivial
> * change in rename(),
> * new option
> * docs.
> Test code:
> * need to clear this option for rename contract tests
> * need to create a new FS with this set to verify the various failure modes
> trigger it.
>
> If this works we should do the same for ABFS, GCS. Hey, maybe even HDFS
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