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
{
		return tmpDir;
	}
	/**
	 * set Dte temporary dir.
	 * @param tmpdir
	 */
	public void setTmpdir( String tmpdir )
	{
		this.tmpDir = tmpdir;
	}
	/**
	 * 
	 * @return
	 */
	public IDocArchiveReader getDocReader()
	{
		return this.reader;
	}
	
	/**
	 * 
	 * @return
	 */
	public IDocArchiveWriter getDocWriter()
	{
		return this.writer;
	}
	
	/**