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
private String tmpDir = System.getProperty( "java.io.tmpdir" );
	
	
	public final static int VERSION_INFO_STREAM = 11;
	
	public final static int DATASET_DATA_STREAM = 21;
	public final static int DATASET_META_STREAM = 22;
	
	public final static int EXPR_VALUE_STREAM = 31;
	public final static int EXPR_META_STREAM = 32;
	public final static int EXPR_ROWLEN_STREAM = 33;
	
	public final static int GROUP_INFO_STREAM = 41;
	public final static int SUBQUERY_INFO_STREAM = 42;
	
	public final static int QUERY_DEFN_STREAM = 43;
	
	public final static int ORIGINAL_QUERY_DEFN_STREAM = 44;
	
	
	public final static int ROW_INDEX_STREAM = 51;
	
	
	public final static int QUERYID_INFO_STREAM = 61;
	
	
	public final static int SUBQUERY_PARENTINDEX_STREAM = 71;
	
	/**
	 * When mode is MODE_GENERATION, the writer stream of archive will be used.