Re: [xsl] Cheaper to prepend or append an item to a sequence?

[Michael Kay <mike@xxxxxxxxxxxx>]

On 22/02/2011 11:27, Costello, Roger L. wrote:
> Hi Folks,
>
> When adding an item to a sequence, it is: (circle the correct answer)
>
> (a) Cheaper to add the item to the front of the sequence
>
> (b) Cheaper to add the item to the end of the sequence
>
> (c) Costs the same to add the item to the front or to the end
>
> (d) The cost varies depending on the XSLT processor

(d) (As with all performance questions).

It's not even a simple answer if you know the processor. Saxon will 
sometimes detect that appending to a sequence can be done without 
copying, either because the old sequence will never be used again, or 
because both can share the same storage - and even I find it difficult 
to predict the circumstances in which the optimizer will determine that 
such optimizations are feasible.

Also, of course, cost is not one-dimensional: time and space both need 
to be considered.

Michael Kay
Saxonica