[HDFS-8432] Introduce a minimum compatible layout version to allow downgrade in more rolling upgrade use cases.

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 2.8.0, 3.0.0-alpha1
• Component/s: namenode, rolling upgrades
• Target Version/s: 2.8.0
• Hadoop Flags: Reviewed
• Assignee: Chris Nauroth
• Reporter: Chris Nauroth
• Created: 19/May/15 17:50
• Updated: 23/Sep/20 14:11
• Resolved: 06/Jun/15 16:52

Description

Maintain the prior layout version during the upgrade window and reject attempts to use new features until after the upgrade has been finalized. This guarantees that the prior software version can read the fsimage and edit logs if the administrator decides to downgrade. This will make downgrade usable for the majority of NameNode layout version changes, which just involve introduction of new edit log operations.

Issue Links

• breaks: HDFS-11209 SNN can't checkpoint when rolling upgrade is not finalized
• is related to: HDFS-5223 Allow edit log/fsimage format changes without changing layout version
• is related to: HDFS-8593 Calculation of effective layout version mishandles comparison to current layout version in storage.
• is related to: HDFS-14753 Document HDFS-8432 (Introduce a minimum compatible layout version to allow downgrade in more rolling upgrade use cases)