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.tests/test/org/eclipse/birt/data/engine/binding/DataSetCacheTest.java
int appendLen = length - inputLen;
		char[] appendChar = new char[appendLen];
		for ( int i = 0; i < appendLen; i++ )
		{
			appendChar[i] = ' ';
		}
		String result = inputStr + new String( appendChar );
		return result;
	}
	/**
	 * Test the feature of clear cache
	 * @throws BirtException
	 */
	public void testClearCache( ) throws BirtException
	{
		this.dataSet.setCacheRowCount( 4 );
		DataEngineImpl myDataEngine = newDataEngine( );
		assertFalse( getDataSetCacheManager( myDataEngine ).doesLoadFromCache( ) );
		assertFalse( getDataSetCacheManager( myDataEngine ).doesSaveToCache( ) );
		QueryDefinition qd = newReportQuery( );
		rowBeArray = getRowExpr( );
		totalBeArray = getAggrExpr( );
		bindingNameRow = getRowExprName( );
		bindingExprRow = getAggrExprName( );
		prepareExprNameAndQuery( rowBeArray,
				bindingNameRow,
				totalBeArray,
				bindingExprRow,
				qd );
		IQueryResults qr = myDataEngine.prepare( qd, appContextMap )