code: public RocksIterator getIterator(String cfName) {
          synchronized (iterators) {
              RocksIterator it = iterators.get(cfName);
              if (it == null) {
                  ColumnFamilyHandle cfh = getColumnFamilyHandle(cfName);
                  if (cfh == null) {
                      return null;
                  }
                  it = rocksDb.newIterator(cfh, readOptions);
                  iterators.put(cfName, it);
              }
              return it;
          }
      }
docs: Obtains an iterator for a column family.
  
  <p>
  Iterators will be automatically closed by this wrapper.
  </p>
  
  @param cfName
  @return