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 cacheMapManager.getLoadFolder( DataSourceAndDataSet.newInstance( this.dataSourceDesign,
				this.dataSetDesign,
				this.parameterHints ) );
	}
	/**
	 * only for test
	 * 
	 * @return
	 */
	public boolean doesLoadFromCache( )
	{
		if ( needsToCache( dataSetDesign, cacheOption, alwaysCacheRowCount ) == false )
			return false;
		return cacheMapManager.doesLoadFromCache( DataSourceAndDataSet.newInstance( this.dataSourceDesign,
				this.dataSetDesign,
				this.parameterHints ) );
	}
	/**
	 * Notice, this method is only for test, it can not be called unless its use
	 * is for test.
	 */
	public void resetForTest( )
	{
		dataSourceDesign = null;
		dataSetDesign = null;
		cacheOption = DataEngineContext.CACHE_USE_DEFAULT;
		alwaysCacheRowCount = 0;
		this.cacheMapManager.resetForTest( );
	}
	/**