Date: Fri, 13 Aug 2010 15:22:43 +0200 From: Gabor Kovesdan <gabor@FreeBSD.org> To: Matthias Andree <matthias.andree@gmx.de> Cc: freebsd-current@freebsd.org Subject: Re: Official request: Please make GNU grep the default Message-ID: <4C654723.1070503@FreeBSD.org> In-Reply-To: <op.vhdilam91e62zd@balu.cs.uni-paderborn.de> References: <4C6505A4.9060203@FreeBSD.org> <4C650B75.3020800@FreeBSD.org> <op.vhdilam91e62zd@balu.cs.uni-paderborn.de>
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Em 2010.08.13. 13:09, Matthias Andree escreveu: > Gabor Kovesdan wrote on 2010-08-13: > >> Em 2010.08.13. 10:43, Doug Barton escreveu: >>> My reason is simple, performance. While doing some portmaster work >>> recently I was regression testing some changes I made to the --index* >>> options and noticed that things were dramatically slower than the last >>> time I tested those features. Thinking that I had made a programming >>> mistake I dug into my code, and while the regexps that I was using >>> could >>> be tuned for slightly better performance the problem was not in my >>> code. >>> I then installed textproc/gnugrep to compare, and the differences were >>> very dramatic using a highly pessimized test case (finding a match on >>> the last line of INDEX). The script I used to test is at >>> http://people.freebsd.org/~dougb/grep-time-trial.sh.txt and a typical >>> result was: >>> >>> GNU grep >>> Elapsed time: 2 seconds >>> >>> BSD grep >>> Elapsed time: 47 seconds >>> >> Ok, I'll take care of this soon, and make GNU grep default, again >> with a knob to build BSD grep. I agree with you that we cannot allow >> such a big performance drawback but I my measures only showed >> significant differences for very big searches and I didn't imagine >> that it could add up to such a big diference. I'm sorry for the bad >> decision I took making it default. > > Without knowing any of the details (I am not using 9-CURRENT), Gabor, > I suggest that you check the documentation around Google's RE2 library > (which is in C++); there are quite a few bits of information relating > to (including worst-case) performance of regexp matchers, both > directly in the re2 documentation, as well as indirect through links > and references. Might be worth a read, together with profiling Doug's > test case if he could tell you how to reproduce those. > Thanks, Matthias. I haven't looked deeply at this but iirc it uses Perl-syntax. We need an efficient, wchar-aware, POSIX(ish) regex library with a good license and atm only TRE conforms to these criteria. Besides, we need GNU-style regex support, which will have to be added to TRE before we can replace our libc-regex. Gabor
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