Bug 180842 Config memory buffer size in data engine execution.
To tuning the performance, it is necessary for DtE to expose API for clients to config the size of memory it used to store the final result set. A new AppContext string, "org.eclipse.birt.data.cache.memory.size" is proposed. The new appcontext entry only accept positive integer as input, the unit of which would be MB.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/executor/cache/CacheUtil.java
result = -1;
			}
			else
			{
				result = 1;
			}
			return result;
		}
		
		if ( ob1.equals( ob2 ) )
		{
			return result;
		}
		else if ( ob1 instanceof Comparable && ob2 instanceof Comparable )
		{
			Comparable comp1 = (Comparable) ob1;
			Comparable comp2 = (Comparable) ob2;
			
			if ( ob1.getClass( ) != ob2.getClass( ) )
			{
				try
				{
					if ( ob1 instanceof Number && ob2 instanceof Number )
					{
						comp1 = DataTypeUtil.toDouble( ob1 );
						comp2 = DataTypeUtil.toDouble( ob2 );
					}
					else if ( ob1 instanceof Date && ob2 instanceof Date )
					{
						comp1 = DataTypeUtil.toDate( ob1 );