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
{
	private static final String META_DATA_FILE = "metaData.data";
	private static final String END = "$end$";
	private static final String BEGIN = "$begin$";
	
	private int cacheOption;
	
	private int alwaysCacheRowCount;
	
	private IBaseDataSourceDesign dataSourceDesign;
	private IBaseDataSetDesign dataSetDesign;
	private Collection parameterHints;
	private Map appContext;
	
	private CacheMapManager cacheMapManager;
	private DataEngine dataEngine;
	
	private boolean needToMerge;
	/**
	 * Construction
	 */
	public DataSetCacheManager( String tempDir, DataEngine dataEngine )
	{
		dataSourceDesign = null;
		dataSetDesign = null;
		cacheOption = DataEngineContext.CACHE_USE_DEFAULT;