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
* @return
	 */
	private Class getTypeClass( int typeCode )
	{
		return DataType.getClass( typeCode );
	}
	/**
	 * Gets the size of the temp customer columns
	 * 
	 * @param metaData
	 * @return
	 * @throws BirtException
	 */
	private int getTempColumnSize( IResultMetaData metaData )
			throws BirtException
	{
		int size = 0;
		for ( int i = 1; i <= metaData.getColumnCount( ); i++ )
		{
			if ( isTempColumn( metaData.getColumnName( i ) ) )
			{
				size++;
			}
			else
			{
				assert ( size == 0 );
			}
		}
		return size;
	}