GNU bug report logs - #21763
poor performance since grep 2.19 when comparing files with grep

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From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Norihiro Tanaka <noritnk <at> kcn.ne.jp>
Cc: 21763-done <at> debbugs.gnu.org, 22357-done <at> debbugs.gnu.org, sur-behoffski <sur_behoffski <at> grouse.com.au>, "L.A. Walsh" <law <at> tlinx.org>, JQK <jquan <at> redhat.com>, 22239 <at> debbugs.gnu.org, Trevor Cordes <gnu <at> tecnopolis.ca>, Bruno Haible <bruno <at> clisp.org>, Ond?ej Cifka <ondra <at> cifka.com>
Subject: bug#21763: bug#22239: bug#22357: grep -f not only huge memory usage, but also huge time cost
Date: Mon, 26 Dec 2016 12:07:49 -0800

[Message part 1 (text/plain, inline)]

Norihiro Tanaka wrote:
> Hmm, how about the following test cases, although it is extreame?

I don't think we need to worry about performance for the case when -w is given, 
and a pattern matches data that contains non-word characters. In practice, such 
cases are rare. I expect that most users would be surprised that -w can match 
non-word characters, and that users wouldn't object to -w rejecting such matches 
(if this wouldn't hurt performance significantly).

While looking into this I did find a very small performance tweak for the test 
case, and installed the attached.

[0001-grep-minor-performance-tweak-for-pure-functions.patch (text/x-diff, attachment)]

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