public SharedIteratorSpaceDataSourceDecorator(SpaceDataSource spaceDataSource,long timeToLive){
  _spaceDataSource=spaceDataSource;
  _timeToLive=timeToLive;
  _queryToSources=new ConcurrentHashMap<DataSourceSQLQuery,SharedDataIteratorSource<Object>>();
  _sourcesToQuery=new ConcurrentHashMap<SharedDataIteratorSource<Object>,DataSourceSQLQuery>();
}

public SharedIteratorSpaceDataSourceDecorator ( SpaceDataSource spaceDataSource , long timeToLive ) { _spaceDataSource = spaceDataSource ; _timeToLive = timeToLive ; _queryToSources = new ConcurrentHashMap < DataSourceSQLQuery , SharedDataIteratorSource < Object > > ( ) ; _sourcesToQuery = new ConcurrentHashMap < SharedDataIteratorSource < Object > , DataSourceSQLQuery > ( ) ; }
create a new instance
