Re: Official request: Please make GNU grep the default

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