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/CacheMapManager.java
return null;
		IResultClass rsClass;
		FileInputStream fis1 = null;
		BufferedInputStream bis1 = null;
		try
		{
			fis1 = new FileInputStream( folder + "/metaData.data" );
			bis1 = new BufferedInputStream( fis1 );
			IOUtil.readInt( bis1 );
			rsClass = new ResultClass( bis1 );
			bis1.close( );
			fis1.close( );
			return rsClass;
		}
		catch ( FileNotFoundException e )
		{
			throw new DataException( ResourceConstants.DATASETCACHE_LOAD_ERROR,
					e );
		}
		catch ( IOException e )
		{
			throw new DataException( ResourceConstants.DATASETCACHE_LOAD_ERROR,
					e );
		}
	}
	/**
	 * 
	 * @param dsAndDs
	 * @return
	 */