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/impl/PreparedDataSourceQuery.java
/**
	 * @param dataEngine
	 * @param queryDefn
	 * @param dataSetDesign
	 * @throws DataException
	 */
	PreparedDataSourceQuery( DataEngineImpl dataEngine,
			IQueryDefinition queryDefn, IBaseDataSetDesign dataSetDesign,
			Map appContext )
			throws DataException
	{
		this.dataSetDesign = dataSetDesign;
		this.queryDefn = queryDefn;
		this.dataEngine = dataEngine;
		this.appContext = appContext;
		
		preparedQuery = new PreparedQuery( dataEngine.getSession( ),dataEngine.getContext( ),
				queryDefn,
				this,
				appContext );
	}
	
	/**
	 * @param dataEngine
	 * @param baseQueryDefn
	 * @param queryDefn
	 * @param dataSetDesign
	 * @param appContext
	 * @throws DataException