(AutoIt) XML Path Performance Optimizations

Discusses some important things to know about using Chilkat paths in the Chilkat XML API.

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$oXml = ObjCreate("Chilkat.Xml")

; Let's load XML containing the following:

; <?xml version="1.0" encoding="utf-8"?>
; <xyz>
;     <licenses>
;         <license>
;             <id>1234</id>
;         </license>
;         <license>
;             <id>1234</id>
;         </license>
; ...
; My sample XML contains 64,000 "license" nodes ..
; ...
;         <license>
;             <id>1234</id>
;         </license>
;         <license>
;             <id>1234</id>
;         </license>
;     </licenses>
; </xyz>
; 
Local $bSuccess = $oXml.LoadXmlFile("qa_output/large.xml")
If ($bSuccess <> True) Then
    ConsoleWrite($oXml.LastErrorText & @CRLF)
    Exit
EndIf

; Iterating over the individual "license" nodes with this code snippet is
; extremely slow:
Local $iLicCount = $oXml.NumChildrenHavingTag("licenses|license")
ConsoleWrite("license count = " & $iLicCount & @CRLF)

Local $s
Local $i = 0
; If "10" is changed to licCount, then it becomes apparent that this loop gets slower with each iteration.
While $i < 10
    $oXml.I = $i
    $s = $oXml.GetChildContent("licenses|license[i]|id")
    ConsoleWrite($i & ": " & $s & @CRLF)
    $i = $i + 1
Wend

; The reason it is extremely slow is that the "license[i]" part of the path passed to GetChildContent
; says: find the i'th child of "licenses" having the tag "license".  Chilkat cannot assume that all
; children of an XML node have the same tag.  Therefore it's not possible to directly access the i'th child.
; Internally, Chilkat must start at the 1st child and iterate until it reaches the i'th child having the
; tag "license".

; For example, imagine if the XML was like this:

; <?xml version="1.0" encoding="utf-8"?>
; <xyz>
;     <licenses>
;         <license>
;             <id>1234</id>
;         </license>
;         <somethingElse>
;             <a>abc</a>
;         </somethingElse>
;         <license>
;             <id>1234</id>
;         </license>
; ...

; In the above XML, the 1st "license" is the 1st child of "licenses", but the 2nd "license"
; is the 3rd child of "licenses".

; If you already know that all children have the same tag, there is a shortcut that allows
; for direct access to that child.  Just leave off the tag name, like this:

$i = 0
; If "10" is changed to licCount, then we can see the time for each loop is the same, and it's fast.
While $i < 10
    $oXml.I = $i
    $s = $oXml.GetChildContent("licenses|[i]|id")
    ConsoleWrite($i & ": " & $s & @CRLF)
    $i = $i + 1
Wend

; When we pass just the index "[i]", we're saying: Get the i'th child regardless of tag.
; This is extremely fast because internally we can just access the i'th child directly.

; Another performance improvement is to call NumChildrenAt rather than NumChildrenHavingTag.
; For example:
$iLicCount = $oXml.NumChildrenAt("licenses")
ConsoleWrite("licCount = " & $iLicCount & @CRLF)

; NumChildrenAt returns the total number of children at the tag path.  If we already know
; all children will have the same tag, we can just get the count