Subject: Re: [xsl] how to estimate speed of a transformation From: Niko Matsakis <niko@xxxxxxxxxxxxx> Date: Thu, 11 Dec 2003 09:21:14 -0500 (EST) |
In my experience developing an optimizing XSLT compiler, things like tail recursion and the obvious optimizations are not the biggest performance killers. Instead, it is the fact that language requires you to express many concepts as expensive loops that iterate over far more nodes than are necessary. This is not a criticism of the language; I enjoy XSLT, and I know the benefits of a functional design, but it is a fact that most of the art of truly optimizing XSLT involves divining what the user wants you to do and doing it differently from how it was expressed in the .xsl file. Also, you should keep in mind that C/C++ compilers have been around for a long time and all those optimizations that you take for granted, such as constant folding, loop strength reduction, etc, were by no means universal when the art was young. XSLT interpreters and compilers are relatively young, and I'm sure that as the language matures, a standard set of opimizations will grow and be more reliable. We don't know yet what the best optimizations for XSLT are; things like tail recursion are a good idea, but they are not the holy grail of XSLT optimization. Furthermore, optimizations like memoization are not always wins; it may be good for your test case, but other tests will show slow downs and unnecessary memory use. <shameless-plug>If you are really interested in top notch XSLT performance, you should check out DataPower's XA35/XS40. It is powered by an XSLT JIT compiler specifically intended to provide excellent performance. If performance is really important to you, it's worth a look. We also have a built-in XSLT profiler, support for exslt extensions, etc.</shameless-plug> my 2 cents, Niko XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
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