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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-16090) S3A Client to add explicit support for versioned stores
Date Tue, 19 Mar 2019 10:50:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-16090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16795967#comment-16795967
] 

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

BTW, in future, with a move to async operations, I could imagine that write context doing
the scan for parent dirs happening asynchronously with the file write. Assuming the write
takes less than a few seconds, and 200ms per probe, if you have enough httpclient connections
there'd be no delay at the end of the write at all. 

Some risk of multiple writes to same dir finding entries which will be deleted anyway, so
spurious tombstones created. Unless before that final bulk delete did a getObjectMetada call
on the first marker believed to exist, and, if found, assume there's been a bulk delete already

> S3A Client to add explicit support for versioned stores
> -------------------------------------------------------
>
>                 Key: HADOOP-16090
>                 URL: https://issues.apache.org/jira/browse/HADOOP-16090
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3
>    Affects Versions: 2.8.1
>            Reporter: Dmitri Chmelev
>            Assignee: Steve Loughran
>            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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