[GitHub] [shardingsphere] azexcy opened a new issue, #24150: JDBC streaming query parameter may not actually take effect

Mon, 13 Feb 2023 18:22:36 -0800 


azexcy opened a new issue, #24150:
URL: https://github.com/apache/shardingsphere/issues/24150

   ## Question
   
   When i use streaming query at `ShardingSphere-JDBC`, it's may not take 
effect. whether it takes effect is controlled by `ConnectionMode` at 
ExecuteQueryCallback
   <img width="1296" alt="image" 
src="https://user-images.githubusercontent.com/101622833/218620872-5fa7dd7c-39bd-49a0-a533-e2849873eab8.png";>
   
   The JDBCMemoryQueryResult will load all records at memory, not like 
streaming query.
   ```
   public final class JDBCMemoryQueryResult extends AbstractMemoryQueryResult {
       
       public JDBCMemoryQueryResult(final ResultSet resultSet, final 
DatabaseType databaseType) throws SQLException {
           super(new JDBCQueryResultMetaData(resultSet.getMetaData()),
                   
TypedSPILoader.getService(DialectQueryResultDataRowLoader.class, 
databaseType.getType()).load(resultSet.getMetaData().getColumnCount(), 
resultSet));
       }
   }
   
   public abstract class AbstractQueryResultDataRowLoader implements 
DialectQueryResultDataRowLoader {
       
       @Override
       public Collection<MemoryQueryResultDataRow> load(final int columnCount, 
final ResultSet resultSet) throws SQLException {
           Collection<MemoryQueryResultDataRow> result = new LinkedList<>();
           while (resultSet.next()) {
               List<Object> rowData = new ArrayList<>(columnCount);
               for (int columnIndex = 1; columnIndex <= columnCount; 
columnIndex++) {
                   Object rowValue = loadRowValue(resultSet, columnIndex);
                   rowData.add(resultSet.wasNull() ? null : rowValue);
               }
               result.add(new MemoryQueryResultDataRow(rowData));
           }
           return result;
       }
   ```
   
   the `ConnectionMode` value depend on maxConnectionsSizePerQuery, (default 
value is 1).
   
   <img width="1405" alt="image" 
src="https://user-images.githubusercontent.com/101622833/218621061-1864c627-c2a6-4dc7-b15d-fa95c34d8180.png";>
   
   If i want to use the streaming query, is there a better way increasing 
maxConnectionsSizePerQuery (because the size of this value is not easy to set)?
   
   eg. MySQL streaming query parameter
   ```
          PreparedStatement result = connection.prepareStatement(sql, 
ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
           result.setFetchSize(Integer.MIN_VALUE);
           return result;
   ```


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