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https://issues.apache.org/jira/browse/HIVE-15093?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15616031#comment-15616031
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Thomas Poepping commented on HIVE-15093:
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Shouldn't this be implemented in s3a? There could be many other instances where
Hive attempts to rename a directory, and there is much potential in the future
for this to be implemented wrongly.
In addition, other Hadoop-stack applications may also have a use case for
blobstore->blobstore renames. Should we place the burden on them to implement
this themselves?
Also, what if there is some new type of filesystem coming in the future, that
requires some other implementation of move. Do we want to set the precedent of
a large tree of if/else based on filesystem?
Seems that the more correct solution would be to allow s3a to be smart about
seeing that it's a rename from blobstore directory->blobstore directory, and
use a threadpool in that case.
Thoughts?
> For S3-to-S3 renames, files should be moved individually rather than at a
> directory level
> -----------------------------------------------------------------------------------------
>
> Key: HIVE-15093
> URL: https://issues.apache.org/jira/browse/HIVE-15093
> Project: Hive
> Issue Type: Sub-task
> Components: Hive
> Affects Versions: 2.1.0
> Reporter: Sahil Takiar
> Assignee: Sahil Takiar
> Attachments: HIVE-15093.1.patch
>
>
> Hive's MoveTask uses the Hive.moveFile method to move data within a
> distributed filesystem as well as blobstore filesystems.
> If the move is done within the same filesystem:
> 1: If the source path is a subdirectory of the destination path, files will
> be moved one by one using a threapool of workers
> 2: If the source path is not a subdirectory of the destination path, a single
> rename operation is used to move the entire directory
> The second option may not work well on blobstores such as S3. Renames are not
> metadata operations and require copying all the data. Client connectors to
> blobstores may not efficiently rename directories. Worst case, the connector
> will copy each file one by one, sequentially rather than using a threadpool
> of workers to copy the data (e.g. HADOOP-13600).
> Hive already has code to rename files using a threadpool of workers, but this
> only occurs in case number 1.
> This JIRA aims to modify the code so that case 1 is triggered when copying
> within a blobstore. The focus is on copies within a blobstore because
> needToCopy will return true if the src and target filesystems are different,
> in which case a different code path is triggered.
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