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
else
					sql = null;
			}
		}
		return sql;
	}
	/**
	 * Reset the QueryText content
	 * 
	 * @param text
	 * @return the new String containing timestamp information
	 * @throws IOException
	 * @throws DataException
	 * @throws ClassNotFoundException
	 */
	private String resetQueryText( String text ) throws IOException,
			DataException, ClassNotFoundException
	{
		String timestamp = CacheUtil.getLastTime( this.getSaveFolder( ) );
		if ( timestamp == null || timestamp.length( ) != 14 )
		{
			return null;
		}
		return text.replaceAll( "\\Q${DATE}$\\E", timestamp );
	}
	/**
	 * Util class to help merge delta data with the local existed data and
	 * update the revalent information in cache file.
	 */
	private class MergeUtil