[QPID-6996] Can't make a node master twice (during a single Broker lifetime)

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 0.30, 0.32, qpid-java-6.0
• Fix Version/s: qpid-java-6.0.1, qpid-java-6.1
• Component/s: Broker-J
• Assignee: Unassigned
• Reporter: Keith Wall
• Created: 13/Jan/16 14:13
• Updated: 02/Oct/19 19:21
• Resolved: 20/Jan/16 13:38

Description

The Java Broker's BDB HA implementation permits the mastership to be transferred around the group. To initiate this change, a user mutates the model attribute "role" on object BDBHAVHN or BDBHARRN to have the value MASTER through a management interface.

If I make this change once, the change is effective. If later the mastership moves again (as a result of a failure and subsequent election or a transfer master elsewhere in the group), the attempt to move the mastership back to this node is ignored (defect).

The issue is that ACO#changeAttributes blocks the subsequent change because it does not know that attribute's value is anything other than MASTER. This is because BDBHAVHN#setRole (happens asynchronously as the mastership changes) updates only the CO view of the attribute (#_role), leaving ACO#_attributes.get(ROLE) with a stale value MASTER. The Broker containing the node needs to be bounce to correct the state problem.

The main use-case for transfer master is to restore the master to its business as usual position following a device failure. This use-case is not affected by this defect.