[HDFS-4996] ClientProtocol#metaSave can be made idempotent by overwriting the output file instead of appending to it

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.1.0-beta, 3.0.0-alpha1
• Fix Version/s: 2.1.0-beta
• Component/s: namenode
• Target Version/s: 2.1.0-beta
• Hadoop Flags: Reviewed
• Release Note: The dfsadmin -metasave command has been changed to overwrite the output file. Previously, this command would append to the output file if it already existed.
• Assignee: Chris Nauroth
• Reporter: Chris Nauroth
• Created: 15/Jul/13 20:55
• Updated: 12/May/16 18:14
• Resolved: 18/Jul/13 22:25

Description

ClientProtocol#metaSave opens its output file for append. This prevents the operation from being idempotent, because retries can cause unpredictable side effects (single copy of the output vs. multiple copies). As discussed on HDFS-4974, the operation could be made idempotent by changing this to open the file for overwrite instead of append.

Issue Links

• relates to: HDFS-4974 Analyze and add annotations to Namenode protocol methods and enable retry