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https://issues.apache.org/jira/browse/HADOOP-18842?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17759383#comment-17759383
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Steve Loughran commented on HADOOP-18842:
-----------------------------------------
Update: no, trying to be dynamic is just over complicated.
* always marshall the commit info to Writable.
* default in memory saves in ByteArrayOutputStream
* to disk saves to a file output stream.
The decision to use disk is made by a config option, and would only need
enabling if scale problems were encountered. Use of the same marshalled format
in both forms of storage ensures consistent code coverage, gives us efficient
storage.
> Support Overwrite Directory On Commit For S3A Committers
> --------------------------------------------------------
>
> Key: HADOOP-18842
> URL: https://issues.apache.org/jira/browse/HADOOP-18842
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 3.4.0
> Reporter: Syed Shameerur Rahman
> Assignee: Syed Shameerur Rahman
> Priority: Major
> Labels: pull-request-available
>
> The goal is to add a new kind of commit mechanism in which the destination
> directory is cleared off before committing the file.
> *Use Case*
> In case of dynamicPartition insert overwrite queries, The destination
> directory which needs to be overwritten are not known before the execution
> and hence it becomes a challenge to clear off the destination directory.
>
> One approach to handle this is, The underlying engines/client will clear off
> all the destination directories before calling the commitJob operation but
> the issue with this approach is that, In case of failures while committing
> the files, We might end up with the whole of previous data being deleted
> making the recovery process difficult or time consuming.
>
> *Solution*
> Based on mode of commit operation either *INSERT* or *OVERWRITE* , During
> commitJob operations, The committer will map each destination directory with
> the commits which needs to be added in the directory and if the mode is
> *OVERWRITE* , The committer will delete the directory recursively and then
> commit each of the files in the directory. So in case of failures (worst
> case) The number of destination directory which will be deleted will be equal
> to the number of threads if we do it in multi-threaded way as compared to the
> whole data if it was done in the engine side.
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