get highest number

[Michael Kay]

> Or switch to a better XQuery processor. I find it hard to 
> imagine why a product should take noticeably longer to 
> evaluate max(//@id) than it takes to evaluate //@id.

Or if you can't do that, try coding it yourself as

declare function local:max($n as xs:double+) {
  if (count($n) eq 1)
  then $n
  else
      let $halfway = count($n) idiv 2
      let $maxleft = local:max($n[position() le $halfway)
      let $maxright = local:max($n[position() gt $halfway)
      return if ($maxleft gt $maxright) then $maxleft else $maxright
};

local:max(//@id/number())

Michael Kay
http://www.saxonica.com/