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
{
		
		private IPreparedDSQuery odiPreparedQuery;
		/**
		 * @return prepared query
		 */
		public IPreparedDSQuery getPreparedOdiQuery( )
		{
			return odiPreparedQuery;
		}
		/*
		 * @see org.eclipse.birt.data.engine.impl.PreparedQuery.Executor#createOdiDataSource()
		 */
		protected IDataSource createOdiDataSource( ) throws DataException
		{
			return null;
		}
		/*
		 * @see org.eclipse.birt.data.engine.impl.PreparedQuery.Executor#createOdiQuery()