@Override
  public boolean clearStream(StreamSpec streamSpec) {
    return false;
  }
Clear the stream described by the spec.
@param streamSpec  The spec for the physical stream on the system.
@return {@code true} if the stream was successfully cleared.
        {@code false} if clearing stream failed.
samza-core/src/main/java/org/apache/samza/system/inmemory/InMemorySystemAdmin.java