public void preBalanceSwitch(final boolean b) throws IOException {
    if (this.coprocEnvironments.isEmpty()) {
      return;
    }
    execOperation(new MasterObserverOperation() {
      @Override
      public void call(MasterObserver observer) throws IOException {
        observer.preBalanceSwitch(this, b);
      }
    });
  }
Invoked after rollback merge regions operation
@param regionsToMerge the regions to merge
@param user           the user
hbase-server/src/main/java/org/apache/hadoop/hbase/master/MasterCoprocessorHost.java