Re: [xslt] XSLT compilation is slow for big XSLTs

[Christian Ceelen <christian ceelen gmail com>]

Hi Nick,

Thank you very much for the answer. That sounds like a very good idea. Yet would the validation still be correct, if the hashtable is local to the stylesheet in which the template was defined? I was wondering what would happen if the same template name is defined in two files, where one of the files then imports or includes the other. Concerning the imports i think the standard is clear, the defined template has lower preference, so having two with the same name sounds legit to me. But what happens when the file is included?

My current understanding is that real validation requires to walk the include tree for each template name. Would that be correctly replicating the existing behavior?

Btw. In xsltInernals.h:L1514 i found in struct _xsltStylesheet:

void *templatesHash; 

Is this table already containing what we want?

Best regards,

Christian

On Wed, Aug 19, 2015 at 1:00 PM, Nick Wellnhofer <wellnhofer aevum de> wrote:

On 19/08/2015 10:47, Christian Ceelen wrote:

At the moment i do not have a deep understanding of the libXSLT code. My
current guess is, that this point at which the template name is validated to
be unique in the stylesheet. The current algorithm seems to be walking
linearly through the list of all already created templates and is comparing
the name with each. Given that the compilation process is walking through all
templates this loop means that we have an O(n^2) algorithm (with n being the
number of template instances in the stylesheet to compile).
The huge number of templates in my XSLTs are just so far over the edge, that
the compilation takes 35s. I ran a test in which i skipped the loop. This
reduced the compilation time to below 2.5 s.

Would anyone let me know if i have understood the code? What can i do to
improve the code that would get easily accepted and released? I am open to any
kind of suggestions on what to do to speed this validation step up with a data
structure or mechanism already existing ?

Yes, template names are verified by searching a linked list which is O(n^2). Template lookup by name uses the same list:

    https://github.com/GNOME/libxslt/blob/master/libxslt/imports.c#L375

It shouldn't be too hard to change the code to use an xmlHashTable:

    https://github.com/GNOME/libxml2/blob/master/include/libxml/hash.h

Simply add a the hash table to struct _xsltStylesheet

    https://github.com/GNOME/libxslt/blob/master/libxslt/xsltInternals.h#L1509

add some initialization and cleanup, then use xmlHashAddEntry2 and xmlHashLookup2 with the template's name and namespace URI. This should make name verification O(n) overall and lookup of a single template by name O(1).

What is now the developer or working repository for libxslt?
I found the git repository on git.gnome.org <http://git.gnome.org>, the
GNOME/libxslt on github, plus several forks which seem to be working repos.
Can you point me please to the repo against which i should use for further
investigation or patches?

The official repo is the one at git.gnome.org:

    https://git.gnome.org/browse/libxslt/

Nick

_______________________________________________
xslt mailing list, project page http://xmlsoft.org/XSLT/
xslt gnome org
https://mail.gnome.org/mailman/listinfo/xslt