Bug 180189 Support in memory data set cache.
Currently, Design-Time Data Cache is stored on disks. By performance tests using ramdisk, we found that caching in physical memory can improve the performance of RunAndRender by 30%.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/PreparedJointDataSourceQuery.java
sortExpression = condition.getRightExpression( );
		}
		SortDefinition sort = new SortDefinition( );
		sort.setExpression( sortExpression.getText( ) );
		preparedQuery.getReportQueryDefn( ).getSorts( ).add( sort );
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.data.engine.impl.PreparedDataSourceQuery#newExecutor()
	 */
	protected QueryExecutor newExecutor( )
	{
		return new JointDataSetQueryExecutor( );
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.birt.data.engine.api.IPreparedQuery#getParameterMetaData()
	 */
	public Collection getParameterMetaData( ) throws BirtException
	{
		return null;
	}
	/**
	 * 
	 * Concrete class of DSQueryExecutor used in PreparedExtendedDSQuery
	 * 
	 */
	private class JointDataSetQueryExecutor extends DSQueryExecutor