HBASE-30300 ADDENDUM: This is a branch-2 only addendum to add throttling time check already present in master and branch-3 (#8516)

Signed-off-by: Tak Lon (Stephen) Wu <taklwu@apache.org>

Author: wchevreuil

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

@@ -322,12 +322,15 @@ private boolean serverHasCacheSpaceForRegion(BalancerClusterState cluster, int r
 
   @Override
   public void throttle(RegionPlan plan) {
-    synchronized (this) {
-      try {
-        // Release the monitor while waiting to avoid blocking other threads.
-        wait(getThrottleDurationMs(plan));
-      } catch (InterruptedException e) {
-        throw new RuntimeException(e);
+    long throttlingTime = getThrottleDurationMs(plan);
+    if (throttlingTime > 0) {
+      synchronized (this) {
+        try {
+          // Release the monitor while waiting to avoid blocking other threads.
+          wait(getThrottleDurationMs(plan));
+        } catch (InterruptedException e) {
+          throw new RuntimeException(e);
+        }
       }
     }
   }