Re: [xml] xpath evaluation timeout

[Zhigang Chen <zhigangc gmail com>]

Thanks Liam

We are building a platform to which codes containing xpaths are submitted by external users. Manual 
optimization of xpaths are infeasible. Do you know about any tools that can automate it?

-
Z


On Oct 18, 2012, at 7:15 PM, Liam R E Quin <liam holoweb net> wrote:

> On Thu, 2012-10-18 at 18:00 -0700, Zhigang Chen wrote:
> > Hi
> >
> > We sometimes run into the situation where a pretty expensive xpath
> > (e.g. .//table//td[ class]) is run on a big document (~ 9M) and it
> > takes very very long. In fact we never see it finish.
>
> [resending from the right account, sorry]
>
> I routinely do queries like that with a 50 MByte document, but with
> XQuery implementations (XPath 2) rather than XPath 1. I get results in
> the order of a few milliseconds.
>
> It would probably be worth adding element indexes to libxml2, even if
> they can't easily be built during parsing.
>
> In the meantime you could try to speed this query up yourself by writing
> it as
>     .//tr[ class]
> or, if this is not HTML.,
>     .//tr[ class][ancestor::table]
>
> Liam
>
> -- 
> Liam Quin - XML Activity Lead, W3C, http://www.w3.org/People/Quin/
> Pictures from old books: http://fromoldbooks.org/
> Ankh: irc.sorcery.net irc.gnome.org freenode/#xml
> Co-author, 5th edition of "Beginning XML", Wrox, July 2012
> -- 
> Liam Quin - XML Activity Lead, W3C, http://www.w3.org/People/Quin/
> Pictures from old books: http://fromoldbooks.org/
> Ankh: irc.sorcery.net irc.gnome.org freenode/#xml