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/PreparedJointDataSourceQuery.java
}
			initialize( dataEngine, appContext );
			JointResultMetadata jrm = getJointResultMetadata( left.getResultMetaData( ),
					right.getResultMetaData( ) );
			resultClass = jrm.getResultClass( );
			populator = JointDataSetPopulatorFactory.getBinaryTreeDataSetPopulator( left.getOdiResult( ),
					right.getOdiResult( ),
					jrm,
					matcher,
					joinType, dataEngine.getSession( ),
					dataSetDesign.getRowFetchLimit( ));
			if ( doesSaveToCache( ) == false )
				return new CachedResultSet( (BaseQuery) this.odiQuery,
						resultClass,
						populator,
						eventHandler, dataEngine.getSession( ) );
			else
				return new CachedResultSet( (BaseQuery) this.odiQuery,
						resultClass,
						new DataSetResultCache( populator, resultClass, dataEngine.getSession( ) ),
						eventHandler, dataEngine.getSession( ) );
		}
		/**
		 * @param obs
		 * @return
		 */
		private List toList( Object[] obs )
		{
			if ( obs == null )
				return null;