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
/**
	 * Clear cache
	 * 
	 * @param dataSourceDesign2
	 * @param dataSetDesign2
	 */
	public void clearCache( IBaseDataSourceDesign dataSourceDesign2,
			IBaseDataSetDesign dataSetDesign2 )
	{
		if ( dataSourceDesign2 == null || dataSetDesign2 == null )
			return;
		DataSourceAndDataSet ds = DataSourceAndDataSet.newInstance( dataSourceDesign2,
				dataSetDesign2,
				null );
		cacheMapManager.clearCache( ds );
	}
	/**
	 * @return
	 */
	public String getSaveFolder( )
	{
		return cacheMapManager.getSaveFolder( DataSourceAndDataSet.newInstance( this.dataSourceDesign,
				this.dataSetDesign,
				this.parameterHints ) );
	}
	/**
	 * @return
	 */
	public String getLoadFolder( )
	{