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
this.dataSet.setCacheRowCount( 4 );
		DataEngineImpl myDataEngine = newDataEngine( );
		assertFalse( getDataSetCacheManager( myDataEngine ).doesLoadFromCache( ) );
		assertFalse( getDataSetCacheManager( myDataEngine ).doesSaveToCache( ) );
		QueryDefinition qd = this.newReportQuery( );
		rowBeArray = getRowExpr( );
		totalBeArray = getAggrExpr( );
		bindingNameRow = getRowExprName( );
		bindingExprRow = getAggrExprName( );
		String[] ccName = new String[]{
				"col0 col1", "\"col0+col1\""
		};
		String[] ccExpr = new String[]{
				"row.AMOUNT", "row.AMOUNT*2"
		};
		for ( int i = 0; i < ccName.length; i++ )
		{
			ComputedColumn computedColumn = new ComputedColumn( ccName[i],
					ccExpr[i],
					DataType.DECIMAL_TYPE );
			( (BaseDataSetDesign) this.dataSet ).addComputedColumn( computedColumn );
		}
		prepareExprNameAndQuery( rowBeArray,
				bindingNameRow,
				totalBeArray,
				bindingExprRow,
				qd );
		IQueryResults qr = myDataEngine.prepare( qd, appContextMap )
				.execute( null );
		qr.getResultIterator( ).next( );