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
|| mode == MODE_PRESENTATION || mode == DIRECT_PRESENTATION || mode == MODE_UPDATE ) )
			throw new DataException( ResourceConstants.RD_INVALID_MODE );
		if ( writer == null && mode == MODE_GENERATION )
			throw new DataException( ResourceConstants.RD_INVALID_ARCHIVE );
		if ( reader == null && mode == MODE_PRESENTATION )
			throw new DataException( ResourceConstants.RD_INVALID_ARCHIVE );
		if ( ( writer == null || reader == null )
				&& mode == MODE_UPDATE )
			throw new DataException( ResourceConstants.RD_INVALID_ARCHIVE );
		this.mode = mode;
		this.scope = scope;
		this.reader = reader;
		this.writer = writer;
		this.cacheOption = CACHE_USE_DEFAULT;
	}
	/** 
	 * @return current context mode
	 */
	public int getMode( )
	{
		return mode;
	}
	/**
	 * @return current top scope
	 */
	public Scriptable getJavaScriptScope( )
	{
		return scope;
	}
	/**