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From "Eugene Koontz (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-5202) NPE in master.AssignmentManager.regionOnline()
Date Sun, 15 Jan 2012 18:23:39 GMT
NPE in master.AssignmentManager.regionOnline()

                 Key: HBASE-5202
                 URL: https://issues.apache.org/jira/browse/HBASE-5202
             Project: HBase
          Issue Type: Bug
    Affects Versions: 0.90.6
            Reporter: Eugene Koontz
            Assignee: Eugene Koontz

The following NPE can occur during master failover:

2012-01-15 17:45:00,314 FATAL [Master:1;ip-10-166-123-193.us-west-1.compute.internal:36708]
master.HMaster(944): Unhandled exception. Starting shutdown.
        at org.apache.hadoop.hbase.master.AssignmentManager.regionOnline(AssignmentManager.java:724)
        at org.apache.hadoop.hbase.master.AssignmentManager.processFailover(AssignmentManager.java:214)
        at org.apache.hadoop.hbase.master.HMaster.finishInitialization(HMaster.java:396)
        at org.apache.hadoop.hbase.master.HMaster.run(HMaster.java:279)
        at java.lang.Thread.run(Thread.java:636)

This is caused by regionOnline() being passed a null serverInfo (its second parameter). 

The AssignmentManager's processFailover() method is passing a null to regionOnline() because
the value that regionOnline is passing, hsi, is set as:

hsi = this.serverManager.getHServerInfo(this.catalogTracker.getMetaLocation());

hsi = this.serverManager.getHServerInfo(this.catalogTracker.getRootLocation());

getHServerInfo(), is defined as:

  public HServerInfo getHServerInfo(final HServerAddress hsa) {
    synchronized(this.onlineServers) {
      // TODO: This is primitive.  Do a better search.
      for (Map.Entry<String, HServerInfo> e: this.onlineServers.entrySet()) {
        if (e.getValue().getServerAddress().equals(hsa)) {
          return e.getValue();
    return null;

This can return null because the onlineServers map does not yet have a value corresponding
to the key supplied by the catalogTracker's getRootLocation() or getMetaLocation(). 

Since the catalogTracker uses zookeeper to establish the server locations of {{-ROOT-}} and
{{.META.}}, while the onlineServers map is set according to the these servers registering
with the master, there can be an inconsistency between the catalogTracker and the onlineServers
if either of these regionservers is online with respect to zookeeper, but haven't yet registered
with the master (perhaps due to a high latency network between the master and the regionserver).

The attached testMasterFailoverWithSlowRS.txt patch can be used to modify TestMasterFailover
to cause this NPE. 

The proposed fix (provided along with the above test in a separate attachment) is for the
master to use the new verifyMetaTablesAreUp() to wait for both of the servers named by the
catalog tracker's getRootLocation() and getMetaLocation() to register with the master before
the master can continue with failover.

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