Re: RE: xslt performance issue position() function use
You are right $p is a string if I use number($p) it also works anyhow that type conversion is not main reason for my perf problem I'm using latest 1.1.17 libxslt , I also tried Xalan but it is two times slower (not to mention that there is some bug in supporting xsl:variable) I tried your suggestion with xsl:variable but there is virtually no difference :-( Maybe this is stupid question but how you can declare variable to be integer type Is below change the answer ??? ;-) the value for $p was assigned this way <xsl:variable name="p" select="./@p"/> when I changed it to <xsl:variable name="p" select="number(./@p)"/> then xslt runs two times faster i.e. from 20sec to 10sec great but still it's way to slow any suggestions ??? BTW such a small change and such improvement it's really amazing :-))) thanks Chris On Fri, 25 Aug 2006 13:08:21 +0100, "Michael Kay" wrote: > Firstly, the fact that ./v[$p] doesn't work, but ./v[$p + 0] does work, > means that the value of $p is not a number. Perhaps it is a string, or > perhaps it is a result tree fragment. Either way, you would probably get an > immediate performance improvement by changing it to be a number, to avoid > the conversion costs each time the value is used. > > Incidentally, the expression "./v" is exactly the same as "v". If your > processor is particularly stupid, the more complex expression might take > longer to evaluate. > > It's of course entirely dependent on your XSLT processor whether the > expression v[$p] takes constant time, or time proportional to $p. It looks > as if in your case, it's taking time proportional to $p. That would be the > case if you were using Saxon. In Saxon you could get round this by using a > variable: > > <xsl:variable name="vseq" select="v"/> > <xsl:for-each.... > <xsl:value-of select="$vseq[$p]" > > But that wouldn't necessarily help on a different processor. Note also that > this only works if $p is known at compile time to be a number - so you need > to fix that problem first. > > Michael Kay > http://www.saxonica.com/ > > > > -----Original Message----- > > From: krzysztof@xxxxxxxxxxxx [mailto:krzysztof@xxxxxxxxxxxx] > > Sent: 25 August 2006 12:20 > > To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx > > Subject: xslt performance issue position() function > > used in predicate very slow > > > > Hi, > > > > I'm processing xml files that have 150kB size they are > > composed from xml blocks that contain 350 elements with int > > values here is example > > > > < obj name="obj1"> > > <v>1</v> > > <v>2</v> > > <v>3</v> > > .... > > <v>350</v> > > </obj> > > > > obj blocks are repeated many times > > in general my xslt selects some set of <v> rows and saves > > in csv format e.g. select 1,2,3,4,15,28,71,17,19 and save to > > csv in my xslt I'm using below expression to select v rows > > > > <xsl:value-of select="./v[position()=$p]"/> > > > > ( in for-each loop I assign value to $p variable) > > > > on P4 2.8 Ghz 512MB ram it takes 20 seconds! to parse 150KB file !!! > > if I comment out this line it takes 1 second so definitely > > it's issue with > > position() > > and selecting this v values. > > > > BTW abbreviated version doesn't wok i.e. select="./v[$p]" > > but select="./v[$p+0]" works is this some bug ??? > > > > Thanks for any tips how to improve performance > > > > Chris
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