Date: Fri, 13 Aug 2010 13:09:00 +0200 From: "Matthias Andree" <matthias.andree@gmx.de> To: freebsd-current@freebsd.org Subject: Re: Official request: Please make GNU grep the default Message-ID: <op.vhdilam91e62zd@balu.cs.uni-paderborn.de> In-Reply-To: <4C650B75.3020800@FreeBSD.org> References: <4C6505A4.9060203@FreeBSD.org> <4C650B75.3020800@FreeBSD.org>
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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. -- Matthias Andree
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