Subject:
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Re: posting weirdness
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Newsgroups:
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lugnet.admin.general
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Date:
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Sun, 17 Dec 2000 16:21:10 GMT
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Viewed:
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282 times
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In lugnet.admin.general, Larry Pieniazek writes:
> No prob. I posted what I wanted to post without the spoiler. Something *is*
> broken, then?
Was, ya.
> > Something about it is chewing up tons and tons
> > of CPU. How many whitespace lines are you putting in?
>
> About a screen and a half worth. Haven't people done spoilers lately???
I was using a regex involving \n\s* which compiled into a nondeterministic
finite-state automata in Perl 5.004 and 5.005. Perl 5.6 is smart enough to
compile it into a deterministic finite-state automata (essentially realising
that \n is part of the \s character class and avoiding a deadly decision tree
trap that results in O(2^n) exponential performance in the NFA case).
The jist of it is that one or two or three newlines in a row chewed up a
millionth of a second of CPU, but twenty newlines in a row chewed up many
seconds of CPU. A screen and a half worth would want to chew up an hour of
CPU, and two screens worth would try to chew up about two months of CPU.
To fix, I changed the regex so to one that has O(n) performance instead of
O(2^n) performance (where n is the number of newlines in a row). Thus, now,
even several pages of newlines still only chew up something on the order of
a millionth of a second of CPU.
I may have other similar regex nasties lurking around (for example in the
news-mail gateway). I'm going to sweep-scan for those now.
--Todd
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Message is in Reply To:
 | | Re: posting weirdness
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| (...) No prob. I posted what I wanted to post without the spoiler. Something *is* broken, then? (...) About a screen and a half worth. Haven't people done spoilers lately??? (...) ++Lar (24 years ago, 17-Dec-00, to lugnet.admin.general)
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