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
rightPrefix
								+ right.getColumnName( i
										- ( left.getColumnCount( ) - leftTempColumnSize ) ),
						rightPrefix
								+ right.getColumnName( i
										- ( left.getColumnCount( ) - leftTempColumnSize ) ),
						getTypeClass( right.getColumnType( i
								- ( left.getColumnCount( ) - leftTempColumnSize ) ) ),
						right.getColumnNativeTypeName( i
								- ( left.getColumnCount( ) - leftTempColumnSize ) ),
						false ) );
			}
			if ( dataSet.getComputedColumns( ) != null )
			{
				for ( int i = 0; i < dataSet.getComputedColumns( ).size( ); i++ )
				{
					IComputedColumn cc = (IComputedColumn) dataSet.getComputedColumns( )
							.get( i );
					index[i
							+ ( left.getColumnCount( ) - leftTempColumnSize )
							+ ( right.getColumnCount( ) - rightTempColumnSize )] = -1;
					columnSource[i
							+ ( left.getColumnCount( ) - leftTempColumnSize )
							+ ( right.getColumnCount( ) - rightTempColumnSize )] = JointResultMetadata.COLUMN_TYPE_COMPUTED;
					projectedColumns.add( new ResultFieldMetadata( i,
							cc.getName( ),
							cc.getName( ),
							DataType.getClass( cc.getDataType( ) ),
							null,
							true ) );