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.tests/test/org/eclipse/birt/data/engine/binding/DataSetCacheTest.java
bindingExprGroup[0] = new ScriptExpression( "dataSetRow.COUNTRY" );
		bindingExprGroup[1] = new ScriptExpression( "dataSetRow.CITY" );
		GroupDefinition[] groupDefn = new GroupDefinition[]{
				new GroupDefinition( "group0" ), new GroupDefinition( "group1" )
		};
		groupDefn[0].setKeyExpression( "row.GROUP_COUNTRY" );
		groupDefn[1].setKeyExpression( "row.GROUP_CITY" );
		QueryDefinition qd = newReportQuery( );
		
		if ( groupDefn != null )
		{
			if ( bindingNameGroup != null )
				for ( int i = 0; i < bindingNameGroup.length; i++ )
					qd.addResultSetExpression( bindingNameGroup[i],
							bindingExprGroup[i] );
			for ( int i = 0; i < groupDefn.length; i++ )
				qd.addGroup( groupDefn[i] );
		}
		
		rowBeArray = getRowExpr( );
		totalBeArray = getAggrExpr( );
		bindingNameRow = getRowExprName( );
		bindingExprRow = getAggrExprName( );
		prepareExprNameAndQuery( rowBeArray,
				bindingNameRow,
				totalBeArray,
				bindingExprRow,
				qd );
		SubqueryDefinition subqueryDefn = new SubqueryDefinition( "IAMTEST",qd );
		subqueryDefn.addResultSetExpression( "COL1",