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Re: [xsl] why matches($title,'.*?(\.|,)\s*$')) can perform so much worse than matches($title,'(\.|,)\s*$'))
2011-07-13 09:14:04
It would be perfectly valid (and sensible) for a query processor to
realise that the two expressions you gave were equivalent and so not
perform n^2 tests, but I am unaware of a processor that makes these
kinds of optimizations to regular expressions.
Actually I've heard it said that there's a wide variation between
different regex engines in how well they handle this kind of thing. See
for example here:
http://swtch.com/~rsc/regexp/regexp1.html
The article at
http://eyalsch.wordpress.com/2009/05/21/regex/
is also useful.
Michael Kay
Saxonica
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