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
* @throws DataException
	 */
	private void initialize( DataEngineImpl dataEngine, Map appContext )
			throws DataException
	{
		int savedCacheOption = getDataSetCacheManager()
				.suspendCache( );
		ResultIterator left = getSortedResultIterator( dataEngine,
				dataSet.getLeftDataSetDesignName( ),
				appContext,
				dataSet.getJoinConditions( ),
				true );
		ResultIterator right = getSortedResultIterator( dataEngine,
				dataSet.getRightDataSetDesignName( ),
				appContext,
				dataSet.getJoinConditions( ),
				false );
		getDataSetCacheManager().setCacheOption( savedCacheOption );
		this.left = left;
		this.right = right;
		this.joinType = dataSet.getJoinType( );
		this.matcher = new JoinConditionMatcher( left.getOdiResult( ),
				right.getOdiResult( ),
				left.getScope( ),
				right.getScope( ),
				dataSet.getJoinConditions( ) );
	}
	/**
	 * Initialize the resultClass. This method is lightweight.
	 *