[HADOOP-13712] S3A open to avoid needless HEAD on the successful execution path

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 2.7.3
• Component/s: fs/s3
• Assignee: Unassigned
• Reporter: Steve Loughran
• Created: 12/Oct/16 10:11
• Updated: 12/Sep/17 09:38
• Resolved: 02/Nov/16 18:27

Description

S3A's open() operation does a getFileStatus() check to see if a file is not a directory before opening with a GET. That initial check will take up at least one HEAD request if the file is present, more if it isn't.

As the GET itself performs the existence check, it is needless. A successful GET of a path which doesn't end in "/" means a file was there. The only reason a getFileStatus call is needed is to choose which error message to display if the path isn't there: is it an FNFE or is it path-is-directory.

Proposed: reorder the code to do the GET; only if that fails fallback to getFileStatus()