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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HADOOP-13829) S3A getContentSummary to use flat listFiles instead of treewalk
Date Wed, 23 Nov 2016 12:03:58 GMT
Steve Loughran created HADOOP-13829:

             Summary: S3A getContentSummary to use flat listFiles instead of treewalk
                 Key: HADOOP-13829
                 URL: https://issues.apache.org/jira/browse/HADOOP-13829
             Project: Hadoop Common
          Issue Type: Sub-task
          Components: fs/s3
    Affects Versions: 2.8.0
            Reporter: Steve Loughran
            Priority: Minor

FS shell {{-count}} uses {{getContentSummary}}  to summarise the contents; this slows significantly
with directory tree depth. On wide directories, as the FileStatus[] array is built up before
recursing down, if there are many millions of files, memory use becomes an issue

Moving to a flat listFiles listing with iterator-based scanning would allow directory depth
to become a near-non-issue, avoid memory problems. We'd need to reverse-construct the directory
tree for its count summary; some hash map of parent paths could build that up while iterating
through the files and adding up their sizes

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