HBASE-12167 NPE in AssignmentManager

hbase-server/src/main/java/org/apache/hadoop/hbase/master/AssignmentManager.java

@@ -1377,6 +1377,9 @@ public class AssignmentManager {
     // Reuse existing assignment info
     Map<ServerName, List<HRegionInfo>> bulkPlan =
       balancer.retainAssignment(regions, servers);
+    if (bulkPlan == null) {
+      throw new IOException("Unable to determine a plan to assign region(s)");
+    }
 
     assign(regions.size(), servers.size(),
       "retainAssignment=true", bulkPlan);
@@ -1404,8 +1407,11 @@ public class AssignmentManager {
     // Generate a round-robin bulk assignment plan
     Map<ServerName, List<HRegionInfo>> bulkPlan
       = balancer.roundRobinAssignment(regions, servers);
-    processFavoredNodes(regions);
+    if (bulkPlan == null) {
+      throw new IOException("Unable to determine a plan to assign region(s)");
+    }
 
+    processFavoredNodes(regions);
     assign(regions.size(), servers.size(),
       "round-robin=true", bulkPlan);
   }

hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java

@@ -1079,13 +1079,28 @@ public class HMaster extends HRegionServer implements MasterServices, Server {
       final List<ServerName> destServers = this.serverManager.createDestinationServersList(
         regionState.getServerName());
       dest = balancer.randomAssignment(hri, destServers);
-    } else {
-      dest = ServerName.valueOf(Bytes.toString(destServerName));
-      if (dest.equals(regionState.getServerName())) {
-        LOG.debug("Skipping move of region " + hri.getRegionNameAsString()
-          + " because region already assigned to the same server " + dest + ".");
+      if (dest == null) {
+        LOG.debug("Unable to determine a plan to assign " + hri);
         return;
       }
+    } else {
+      dest = ServerName.valueOf(Bytes.toString(destServerName));
+      if (dest.equals(serverName) && balancer instanceof BaseLoadBalancer
+          && !((BaseLoadBalancer)balancer).shouldBeOnMaster(hri)) {
+        // To avoid unnecessary region moving later by balancer. Don't put user
+        // regions on master. Regions on master could be put on other region
+        // server intentionally by test however.
+        LOG.debug("Skipping move of region " + hri.getRegionNameAsString()
+          + " to avoid unnecessary region moving later by load balancer,"
+          + " because it should not be on master");
+        return;
+      }
+    }
+
+    if (dest.equals(regionState.getServerName())) {
+      LOG.debug("Skipping move of region " + hri.getRegionNameAsString()
+        + " because region already assigned to the same server " + dest + ".");
+      return;
     }
 
     // Now we can do the move

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/BaseLoadBalancer.java

@@ -858,7 +858,7 @@ public abstract class BaseLoadBalancer implements LoadBalancer {
    * Check if a region belongs to some small system table.
    * If so, it may be expected to be put on the master regionserver.
    */
-  protected boolean shouldBeOnMaster(HRegionInfo region) {
+  public boolean shouldBeOnMaster(HRegionInfo region) {
     return tablesOnMaster.contains(region.getTable().getNameAsString());
   }