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 static final String COLUMN_NAME_SPLITTER = "::";
	private static final String TEMP_COLUMN_STRING = ".*$TEMP_.*";
	
	private IJointDataSetDesign dataSet;
	private IDataSetPopulator populator;
	private IResultClass resultClass;
	private ResultIterator left;
	private ResultIterator right;
	private IJoinConditionMatcher matcher;
	private int joinType;
	private DataEngineImpl dataEngine;