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
/**
	 * Please notice that we must use static variable here for the sharing of
	 * cached data set would be cross data set session.
	 */
	private static Map cacheMap = new HashMap( );
	/**
	 * construction
	 */
	CacheMapManager( String tempDir )
	{
		this.folderUtil = new FolderUtil( );
		this.tempDir = tempDir;
	}
	/**
	 * @return
	 */
	boolean doesSaveToCache( DataSourceAndDataSet dsAndDs )
	{
		String cacheDirStr = null;
		synchronized ( cacheMap )
		{
			cacheDirStr = (String) cacheMap.get( dsAndDs );
		}
		if ( cacheDirStr != null && new File( cacheDirStr ).exists( ) == true )
		{
			return false;
		}
		else
		{
			synchronized ( cacheMap )