Xquery retrieval,3 lines: in-line: 1 sec; in function: 60 seconds

Question

Can anyone point me in the direction to find why 2 similar versions of a search have drastically different execution times?
I've looked at the queryplan of each query and they both use the same index but the queryplans are different.
Is there any documentation on how to read a queryplan, other than the "Getting started guides"
Running on Linux, Ubuntu, Hardy Heron, dbxml 2.4.16
Script passed to dbxml:
#time query '
queryplan '
import module ...
declare copy-namespaces no-preserve, no-inherit;
let $doc_collection := collection("docs.dbxml")
return xslt_browse_content:make_index($doc_collection,"ebs","ac","bk","en-GB","A")
functions:
declare function xslt_browse_content:expand($content as node()*
                                           ,$dom as xs:string
                                           ,$lang as xs:string
                                           ,$node as node()
) as node()* {
  if ($node/self::capdm_text_entity)
  then $content/doc[@lang=$lang and @dom=$dom]/*[@id=$node/@ref]
  else $node
declare function xslt_browse_content:make_index($content as node()*
                                               ,$dom as xs:string
                                               ,$subj as xs:string
                                               ,$comp as xs:string
                                               ,$lang as xs:string
                                               ,$letter as xs:string
) as node()* {
  let $doc := $content/doc[@dom = $dom and
                           @subj = $subj and
                           @comp = $comp and
                           @lang = $lang]
  let $book := $doc/book  
  let $refs := $book/(capdm_text_entity|part/capdm_text_entity)       
  for $r in $refs
  let $c := xslt_browse_content:expand($content,$dom,$lang,$r)
  return $c
  let $c := if ($r/self::capdm_text_entity)
  then $content/doc[@lang=$lang and @dom=$dom]/*[@id=$r/@ref]
  else $r
};If I use xslt_browse_content:expand then it takes 60 seconds.
If I use the commented code it takes ~1 sec.
Thanks,
John Cooper
Edited by: gmfeinberg for formatting

Answer 1

Thanks John,
I look forward to having optimizations cross function boundaries as I'm spending some effort to organize my queries into modules. Mostly, with some fiddling, I can get reasonable performance.
Here's another odd one:
Case 1: takes 0.4 seconds:
let $collection := collection("mpe.dbxml")
let $ui_attr := attribute ui { "action_list" }
| attribute dom {"ifs"}
| attribute subj {"catn"}
| attribute lang {"en-GB"}
| attribute comp {"in"}
let $ui_attr_nm := text{"action"}
| text{"style"}
return product_manager:ui_param($collection/prods/param/*, $ui_attr, $ui_attr_nm)
Case 2: takes 16 seconds
return product_manager:ui_param(collection("mpe.dbxml")/prods/param/*, $ui_attr, $ui_attr_nm)
Case 3: takes 16 seconds
let $param := collection("mpe.dbxml")/prods/param/*
return product_manager:ui_param($param, $ui_attr, $ui_attr_nm)
Is this another case of "optimizing across function boundaries"?
John