[HDFS-5999] Do not create rollback fsimage when it already exists

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Component/s: datanode, ha, hdfs-client, namenode
• Hadoop Flags: Reviewed
• Assignee: Jing Zhao
• Reporter: Jing Zhao
• Created: 23/Feb/14 00:38
• Updated: 23/Feb/14 21:36
• Resolved: 23/Feb/14 21:36

Description

Currently in FSEditLogLoader#applyEditLogOp, if the op is OP_START_LOG_SEGMENT, we do an extra rollback fsimage with condition "totalEdits > 1".

This may cause some issue when we restart a NN with new software. If there is no extra checkpoint after the rollback image, the NN may generate a new rollback image using the new software, and replace the old rollback image. Then later if we want to do rollback the NN, which uses the old software, may not be able to load the rollback image.