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https://issues.apache.org/jira/browse/HADOOP-13208?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15394731#comment-15394731
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Aaron Fabbri commented on HADOOP-13208:
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[~ayousufi] {{listStatus()}} already retrieves file info in batches, and it is
not recursive. This patch is specific to a recursive list operation: It uses
the ability of s3 to list by key (path) prefix to optimize round trips to
accomplish the equivalent of {{ls -R}}.
> S3A listFiles(recursive=true) to do a bulk listObjects instead of walking the
> pseudo-tree of directories
> --------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-13208
> URL: https://issues.apache.org/jira/browse/HADOOP-13208
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Affects Versions: 2.8.0
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Minor
> Attachments: HADOOP-13208-branch-2-001.patch,
> HADOOP-13208-branch-2-007.patch, HADOOP-13208-branch-2-008.patch,
> HADOOP-13208-branch-2-009.patch, HADOOP-13208-branch-2-010.patch,
> HADOOP-13208-branch-2-011.patch, HADOOP-13208-branch-2-012.patch,
> HADOOP-13208-branch-2-017.patch, HADOOP-13208-branch-2-018.patch
>
> Original Estimate: 24h
> Remaining Estimate: 24h
>
> A major cost in split calculation against object stores turns out be listing
> the directory tree itself. That's because against S3, it takes S3A two HEADs
> and two lists to list the content of any directory path (2 HEADs + 1 list for
> getFileStatus(); the next list to query the contents).
> Listing a directory could be improved slightly by combining the final two
> listings. However, a listing of a directory tree will still be
> O(directories). In contrast, a recursive {{listFiles()}} operation should be
> implementable by a bulk listing of all descendant paths; one List operation
> per thousand descendants.
> As the result of this call is an iterator, the ongoing listing can be
> implemented within the iterator itself
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