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
{
			
			folderUtil.deleteDir( cacheDir.get( i ).toString( ) );
		}
	}
	/**
	 * Reset for test case
	 */
	void resetForTest( )
	{
		synchronized ( this )
		{
			cacheMap = new HashMap( );
			folderUtil = new FolderUtil( );
		}
	}
	/**
	 * Return the cached result metadata featured by the given
	 * DataSourceAndDataSet. Please note that the paramter would have no impact
	 * to DataSourceAndDataSet so that will be omited.
	 * 
	 * @param dsAndDs
	 * @return
	 * @throws DataException
	 */
	IResultClass getCachedResultClass( DataSourceAndDataSet dsAndDs )
			throws DataException
	{
		String folder = getMetaDataLoadFolder( dsAndDs );
		if ( folder == null )