[HDFS-957] FSImage layout version should be only once file is complete

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 0.22.0
• Component/s: namenode
• Assignee: Todd Lipcon
• Reporter: Todd Lipcon
• Created: 09/Feb/10 03:55
• Updated: 11/Feb/15 20:05
• Resolved: 11/Feb/15 20:05

Description

Right now, the FSImage save code writes the LAYOUT_VERSION at the head of the file, along with some other headers, and then dumps the directory into the file. Instead, it should write a special IMAGE_IN_PROGRESS entry for the layout version, dump all of the data, then seek back to the head of the file to write the proper LAYOUT_VERSION. This would make it very easy to detect the case where the FSImage save got interrupted.

Issue Links

• is related to: HDFS-955 FSImage.saveFSImage can lose edits
• relates to: HDFS-970 FSImage writing should always fsync before close