use dataset iterator api to reduce driver memory use

Full Scenario OLAP Service/Data Unification Service Outlet

• The query result set should not reasonably have a Limit limit.
• Scenarios answered by hierarchical storage/detailed indexing can support large-scale data exporting
• scenarios answered by query down, querying through JDBC provided by KE, the performance is not significantly lower than using JDBC provided by the data source directly, such as querying Hive JDBC directly.
• the amount of data returned does not set a limit on the number of data entries / or data size, because customer data is growing, the analysis of the scene is not fixed.
• customer behavior using data in a uniform manner, the current asynchronous query in the data use scenarios have limitations.