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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-16090) deleteUnnecessaryFakeDirectories() creates unnecessary delete markers in a versioned S3 bucket
Date Mon, 04 Feb 2019 17:51:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-16090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16760065#comment-16760065
] 

Steve Loughran commented on HADOOP-16090:
-----------------------------------------

bq. Note that issuing a DELETE request without specifying a version ID will always create
a new delete marker, even if one already exists (AWS S3 Developer Guide)

hmmm. This is interesting. 


> deleteUnnecessaryFakeDirectories() creates unnecessary delete markers in a versioned
S3 bucket
> ----------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-16090
>                 URL: https://issues.apache.org/jira/browse/HADOOP-16090
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: fs/s3
>    Affects Versions: 2.8.1
>            Reporter: Dmitri Chmelev
>            Priority: Minor
>
> The fix to avoid calls to getFileStatus() for each path component in deleteUnnecessaryFakeDirectories()
(HADOOP-13164) results in accumulation of delete markers in versioned S3 buckets. The above
patch replaced getFileStatus() checks with a single batch delete request formed by generating
all ancestor keys formed from a given path. Since the delete request is not checking for existence
of fake directories, it will create a delete marker for every path component that did not
exist (or was previously deleted). Note that issuing a DELETE request without specifying
a version ID will always create a new delete marker, even if one already exists ([AWS S3
Developer Guide|https://docs.aws.amazon.com/AmazonS3/latest/dev/RemDelMarker.html])
> Since deleteUnnecessaryFakeDirectories() is called as a callback on successful writes
and on renames, delete markers accumulate rather quickly and their rate of accumulation is
inversely proportional to the depth of the path. In other words, directories closer to the
root will have more delete markers than the leaves.
> This behavior negatively impacts performance of getFileStatus() operation when it has
to issue listObjects() request (especially v1) as the delete markers have to be examined when
the request searches for first current non-deleted version of an object following a given
prefix.
> I did a quick comparison against 3.x and the issue is still present: [https://github.com/apache/hadoop/blob/trunk/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java#L2947|https://github.com/apache/hadoop/blob/trunk/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java#L2947]
>  



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