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/executor/DataSetCacheManager.java
String configFile = getCacheConfig( appContext );
			if ( null != configFile && ( !configFile.equals( "" ) ) )
			{
				String folder = getSaveFolder( );
				File dataFile = new File( folder + File.separator + "data.data" );
				
				
				if ( dataFile.exists( ) )
				{
					File config = new File( configFile );
					FileReader fileReader = null;
					if ( config.exists( ) )
						fileReader = new FileReader( config );
					BufferedReader reader = new BufferedReader( fileReader );
					ArrayList list = readConfigFile( configFile, reader );
					File metaFile = new File( getLoadFolder( )
							+ File.separator + META_DATA_FILE );
					mergeDeltaToFile( dataFile, list, metaFile );
					CacheUtil.saveCurrentTime( getSaveFolder( ) );
					this.needToMerge = false;
				}
			}
		}
		catch ( Exception e )
		{
			throw new DataException( e.getLocalizedMessage( ) );
		}
	}
	/**
	 *