Details

    • Type: Sub-task
    • Status: Open
    • Priority: Minor
    • Resolution: Unresolved
    • Affects Version/s: 2.8.0
    • Fix Version/s: None
    • Component/s: fs/s3
    • Labels:
      None
    • Target Version/s:

      Description

      Currently, S3AFileSystem.getFileStatus(Path f) sends up to 3 requests to S3 when pathToKey(f) = key = "foo/bar" is a directory:

      1. HEAD key=foo/bar [continue if not found]
      2. HEAD key=foo/bar/ [continue if not found]
      3. LIST prefix=foo/bar/ delimiter=/ max-keys=1

      My experience (and generally true, I reckon) is that almost all directories are nonempty directories without a "fake directory" file (e.g. "foo/bar/"). Under this condition, request #2 is mostly unhelpful; it only slows down getFileStatus. Therefore, I propose swapping the order of requests #2 and #3. The swapped HEAD request will be skipped in practically all cases.

      Furthermore, when key = "foo/bar" is a nonempty directory that contains a "fake directory" file (in addition to actual files), getFileStatus currently returns an S3AFileStatus with isEmptyDirectory=true, which is wrong. Swapping will fix this. The swapped LIST request will use max-keys=2 to determine isEmptyDirectory correctly. (Removing the delimiter from the LIST request should make the logic a little simpler than otherwise.)

      Note that key = "foo/bar/" has the same problem with isEmptyDirectory. To fix it, I propose skipping request #1 when key ends with "/". The price is this will, for an empty directory, replace a HEAD request with a LIST request that's generally more taxing on S3.

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        1. HADOOP-13430.001.WIP.patch
          8 kB
          Steven K. Wong

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              • Assignee:
                slider Steven K. Wong
                Reporter:
                slider Steven K. Wong
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                • Created:
                  Updated: