[HDFS-9110] Use Files.walkFileTree in NNUpgradeUtil#doPreUpgrade for better efficiency

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.7.0
• Fix Version/s: 2.8.0, 3.0.0-alpha1
• Target Version/s: 2.8.0
• Assignee: Charlie Helin
• Reporter: Charlie Helin
• Created: 18/Sep/15 20:53
• Updated: 30/Aug/16 01:27
• Resolved: 09/Oct/15 18:49

Description

This is a request to do some cosmetic improvements on top of HDFS-8480. There a couple of File -> java.nio.file.Path conversions which is a little bit distracting.

The second aspect is more around efficiency, to be perfectly honest I'm not sure what the number of files that may be processed. However as HDFS-8480 eludes to it appears that this number could be significantly large.

The current implementation is basically a collect and process where all files first is being examined; put into a collection and after that processed. HDFS-8480 could simply be further enhanced by employing a single iteration without creating an intermediary collection of filenames by using a FileWalker