does anyone tell me why raw measure need dictionary?

[you Zhuang]

I use raw measure to serve original records consults. But why does raw measure 
need dictionary?  If I have a lot of raw measures, performance is slow. I see 
code below :

@Override
public List<TblColRef> getColumnsNeedDictionary(FunctionDesc functionDesc) {
    TblColRef literalCol = functionDesc.getParameter().getColRefs().get(0);
    return Collections.singletonList(literalCol);
}

My raw measures are always double, not big. So I don’t need dictionary at all.

I use raw measures for historical reasons, so I expect someone to tell me why 
and how I can modify to use raw bytes.