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/executor/DataSetCacheManager.java
* Return the cached result metadata. Please note that parameter hint will
	 * not change the returned metadata.
	 * 
	 * @return
	 * @throws DataException
	 */
	public IResultMetaData getCachedResultMetadata(
			IBaseDataSourceDesign dataSource, IBaseDataSetDesign dataSet )
			throws DataException
	{
		IResultClass resultClass = this.cacheMapManager.getCachedResultClass( DataSourceAndDataSet.newInstance( dataSource,
				dataSet,
				null ) );
		if ( resultClass != null )
			return new ResultMetaData( resultClass );
		else
			return null;
	}
	/**
	 * Do the action "merging" when the user provide a specific and valid
	 * configure file
	 * 
	 * @throws BirtException
	 * @throws IOException
	 * @throws ClassNotFoundException
	 */
	private void mergeDelta( ) throws DataException
	{
		try
		{