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/api/DataEngineContext.java
*/
	public void dropStream( String streamPath )
	{
		if ( writer != null )
			writer.dropStream( streamPath );
	}
	/**
	 * According to the paramters of streamID, subStreamID and streamType, an
	 * input stream will be created for it. To make stream close simply, the
	 * stream needs to be closed by caller, and then caller requires to add
	 * buffer stream layer when needed.
	 * 
	 * @param streamID
	 * @param subStreamID
	 * @param streamType
	 * @return input stream for specified streamID, subStreamID and streamType
	 */
	public InputStream getInputStream( String streamID, String subStreamID,
			int streamType ) throws DataException
	{
		assert reader != null;
		String relativePath = getPath( streamID, subStreamID, streamType );
		
		try
		{
			InputStream inputStream = reader.getStream( relativePath );
			
			if ( inputStream == null )
				throw new DataException( ResourceConstants.RD_LOAD_STREAM_ERROR );