[HBASE-13814] AssignmentManager does not write the correct server name into Zookeeper when unassign region

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Won't Fix
• Affects Version/s: 0.94.27
• Component/s: Region Assignment
• Assignee: Unassigned
• Reporter: Jianwei Cui
• Created: 30/May/15 08:46
• Updated: 24/Jun/22 19:19
• Resolved: 05/Jun/21 15:08

Description

When moving region, the region will firstly be unassigned from corresponding region server by the method AssignmentManager#unassign(). AssignmentManager will write the region info and the server name into Zookeeper by the following code:

          versionOfClosingNode = ZKAssign.createNodeClosing(
            master.getZooKeeper(), region, master.getServerName());

It seems that the AssignmentManager misuses the master's name as the server name. If the ROOT region is being moved and the region server holding the ROOT region is just crashed. The Master will try to start a MetaServerShutdownHandler if the server is judged as holding meta region. The judgment will be done by the method AssignmentManager#isCarryingRegion, and the method will firstly check the server name in Zookeeper:

    ServerName addressFromZK = (data != null && data.getOrigin() != null) ?
      data.getOrigin() : null;
    if (addressFromZK != null) {
      // if we get something from ZK, we will use the data
      boolean matchZK = (addressFromZK != null &&
        addressFromZK.equals(serverName));

The wrong server name from Zookeeper will make the server not be judged as holding the ROOT region. Then, the master will start a ServerShutdownHandler. Unlike MetaServerShutdownHandler, the ServerShutdownHandler won't assign ROOT region firstly, making the ROOT region won't be assigned forever. In our test environment, we encounter this problem when moving ROOT region and stopping the region server concurrently.