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

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Message #31 received at 21763-done <at> debbugs.gnu.org (full text, mbox):

From: Norihiro Tanaka <noritnk <at> kcn.ne.jp>
To: Paul Eggert <eggert <at> cs.ucla.edu>
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: Re: bug#22239: bug#22357: grep -f not only huge memory usage,
 but also huge time cost
Date: Mon, 26 Dec 2016 21:06:55 +0900

On Fri, 23 Dec 2016 17:38:42 -0800
Paul Eggert <eggert <at> cs.ucla.edu> wrote:

> No. Thanks, I hadn't considered that possibility. I looked into the
> slowdown and installed the attached patches, which cause 'grep' to
> run about as fast on this test case as grep 2.25 (though not as fast
> as grep 2.26). The main fix is in patch 5. On my platform:

Hmm, how about the following test cases, although it is extreame?

$ cat pat
0
00 0
00 00 0
00 00 00 0
00 00 00 00 0
00 00 00 00 00 0
00 00 00 00 00 00 0
00 00 00 00 00 00 00 0
00 00 00 00 00 00 00 00 0
00 00 00 00 00 00 00 00 00 0
00 00 00 00 00 00 00 00 00 00 0
00 00 00 00 00 00 00 00 00 00 00 0
00 00 00 00 00 00 00 00 00 00 00 00 0
00 00 00 00 00 00 00 00 00 00 00 00 00 0
$ yes '00 00 00 00 00 00 00 00 00 00 00 00 00' |
  head -1000000 >inp
$ time -p env LC_ALL=C src/grep -w -f pat inp

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