AW: [xml] extremely long xslt transformation times

[Steinborn Thomas <Thomas Steinborn erl8 siemens de>]

<snip intro>

> > The compiled XPath is
> > SORT
> >     UNION
> >             COLLECT attrs all
> >             COLLECT nodes all
> >
> > Now we see three different ways to improve performance in this case:
> >
> > 1) optimize the XPath compilation not to sort since the 
> collected node sets
> > are already sorted and the union will not change that
>
>   Err, in general the union operator will force a sort, this is a 
> specific case which seems hard to generalize.
>
> > 3) Avoid sorting a node set by adding a flag to the xmlXPathNodeSet
> > structure if the set is sorted already
>
>   Okay but the merge operation of the union in general will 
> require another
> sort so, how do you compute that a priori
>
> > We'd like to ask the list what approache we should take for 
> this case?
>
>   2 sounds impossible technically, I don't want to change the format
> of the in-memory representation. 1 and 3 are okay at an architectural
> level but I don't see how to do this easilly in practice. But if you
> know how to do this, feel free to work on it, I take patches !

Okay, so if the UNION operator sorts the result set that top level 
sort is not needed, right?

What about COLLECTS, they deliver sorted results as well? If so, maybe we
can optimize more?

Thomas