HBASE-25836 RegionStates#getAssignmentsForBalancer should only care about OPEN or OPENING regions

RegionStates#getAssignmentsForBalancer is used by the HMaster to
collect all regions of interest to the balancer for the next chore
iteration. We check if a table is in disabled state to exclude
regions that will not be of interest (because disabled regions are
or will be offline) or are in a state where they shouldn't be
mutated (like SPLITTING). The current checks are not actually
comprehensive.

Filter out regions not in OPEN or OPENING state when building the
set of interesting regions for the balancer to consider. Only
regions open (or opening) on the cluster are of interest to
balancing calculations for the current iteration. Regions in all
other states can be expected to not be of interest – either offline
(OFFLINE, or FAILED_*), not subject to balancer decisions now
(SPLITTING, SPLITTING_NEW, MERGING, MERGING_NEW), or will be
offline shortly (CLOSING) – until at least the next chore
iteration.

Author: apurtell

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

@@ -36,7 +36,6 @@
 import org.apache.hadoop.hbase.ServerName;
 import org.apache.hadoop.hbase.TableName;
 import org.apache.hadoop.hbase.client.RegionInfo;
-import org.apache.hadoop.hbase.client.TableState;
 import org.apache.hadoop.hbase.master.RegionState;
 import org.apache.hadoop.hbase.master.RegionState.State;
 import org.apache.hadoop.hbase.master.TableStateManager;
@@ -571,23 +570,25 @@ public ServerName getRegionServerOfRegion(RegionInfo regionInfo) {
    * wants to iterate this exported list.  We need to synchronize on regions
    * since all access to this.servers is under a lock on this.regions.
    *
-   * @return A clone of current assignments.
+   * @return A clone of current open or opening assignments.
    */
   public Map<TableName, Map<ServerName, List<RegionInfo>>> getAssignmentsForBalancer(
       TableStateManager tableStateManager, List<ServerName> onlineServers) {
     final Map<TableName, Map<ServerName, List<RegionInfo>>> result = new HashMap<>();
     for (RegionStateNode node : regionsMap.values()) {
-      if (isTableDisabled(tableStateManager, node.getTable())) {
-        continue;
-      }
-      if (node.getRegionInfo().isSplitParent()) {
+      // When balancing, we are only interested in OPEN or OPENING regions and expected
+      // to be online at that server until possibly the next balancer iteration or unless
+      // we decide to move it. Other states are not interesting as the region will either
+      // be closing, or splitting/merging, or will not be deployed.
+      if (!(node.isInState(State.OPEN)||node.isInState(State.OPENING))) {
         continue;
       }
       Map<ServerName, List<RegionInfo>> tableResult =
           result.computeIfAbsent(node.getTable(), t -> new HashMap<>());
       final ServerName serverName = node.getRegionLocation();
+      // A region in ONLINE or OPENING state should have a location.
       if (serverName == null) {
-        LOG.info("Skipping, no server for " + node);
+        LOG.warn("Skipping, no server for " + node);
         continue;
       }
       List<RegionInfo> serverResult =
@@ -603,12 +604,6 @@ public Map<TableName, Map<ServerName, List<RegionInfo>>> getAssignmentsForBalanc
     return result;
   }
 
-  private boolean isTableDisabled(final TableStateManager tableStateManager,
-      final TableName tableName) {
-    return tableStateManager.isTableState(tableName, TableState.State.DISABLED,
-      TableState.State.DISABLING);
-  }
-
   // ==========================================================================
   //  Region in transition helpers
   // ==========================================================================