@Override
  public RSGroupInfo getRSGroupForTable(TableName tableName) throws IOException {
    return holder.tableName2Group.get(tableName);
  }
Update cache of rsgroups. Caller must be synchronized on 'this'.
@param currentGroups Current list of Groups.
hbase-server/src/main/java/org/apache/hadoop/hbase/rsgroup/RSGroupInfoManagerImpl.java