[HDFS-3725] Fix QJM startup when individual JNs have gaps

• Type: Sub-task
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: QuorumJournalManager (HDFS-3077)
• Fix Version/s: QuorumJournalManager (HDFS-3077)
• Component/s: ha
• Target Version/s: QuorumJournalManager (HDFS-3077)
• Hadoop Flags: Reviewed
• Assignee: Todd Lipcon
• Reporter: Todd Lipcon
• Created: 26/Jul/12 00:51
• Updated: 30/Jul/12 23:36
• Resolved: 30/Jul/12 23:36

Description

This fixes a bug in the HDFS-3077 branch:
If one of the JNs goes down and comes back up, it may have a discontiguous set of logs in its storage directories. This means that a future getEditLogManifest call will return a manifest that has gaps - eg it may have txn 1-3 and 7-9 but be missing 4-6. This is OK because it's guaranteed that a quorum of JNs do have those edits elsewhere.

This situation currently causes an exception since the RemoteEditLogManifest constructor verifies that the returned log files form a contiguous set of edits. That was true for the NameNode but no longer true for this new usage.