Re: why matches($title,'.?(\.|,)\s$')) can perform s

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Subject: Re: why matches($title,'.*?(\.|,)\s*$')) can perform so much worse than matches($title,'(\.|,)\s*$'))
From: Michael Kay <mike@xxxxxxxxxxxx>
Date: Wed, 13 Jul 2011 15:13:47 +0100

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

Current Thread

why matches($title,'.*?(\.|,)\s*$')) can perform so much worse than matches($title,'(\.|,)\s*$'))
- Alex Muir - 12 Jul 2011 16:26:58 -0000
  - Oliver Hallam - 13 Jul 2011 12:36:49 -0000
    - Alex Muir - 13 Jul 2011 12:55:27 -0000
    - Michael Kay - 13 Jul 2011 14:14:04 -0000 <=
      - Oliver Hallam - 13 Jul 2011 17:46:37 -0000
      - Michael Kay - 13 Jul 2011 18:17:55 -0000
      - Oliver Hallam - 13 Jul 2011 18:56:39 -0000
      - Liam R E Quin - 13 Jul 2011 23:13:08 -0000

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Re: why matches($title,'.?(\, Alex Muir*	Thread	Re: why matches($title,'.?(\, Oliver Hallam*
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