Date: Sun, 2 Jun 2013 13:16:07 +0100 From: Chris Rees <crees@FreeBSD.org> To: Eduardo Morras <emorrasg@yahoo.es> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: sed query Message-ID: <CADLo838H6ikpO8mSh%2Bu6caZTRYfm56qMgq6%2Bzn2BJoVXZHSNdg@mail.gmail.com> In-Reply-To: <20130602124127.6c3a847ea5ddb116a69d4814@yahoo.es> References: <CADLo838JALaTwdSjy%2BV0JMHkbz1mD%2BezOq7a=dRzeNaSeUrDEg@mail.gmail.com> <20130602124127.6c3a847ea5ddb116a69d4814@yahoo.es>
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On 2 June 2013 11:41, Eduardo Morras <emorrasg@yahoo.es> wrote: > On Fri, 31 May 2013 15:01:59 +0100 > Chris Rees <utisoft@gmail.com> wrote: > >> Hi all, >> >> I think I've discovered a strange behaviour of sed perhaps triggered >> by the length of a regex passed to it. I noticed that a certain >> expression I passed took a very long time, and suspected the usual >> backtracking loop, so I started trimming it... and discovered this: >> >> [crees@pegasus]~% time sed -ne "s,^BitchX-[0-9][^|]*[\|]/usr/por,," >> /var/db/pkg/INDEX-9 >> 4.699u 0.007s 0:04.70 99.7% 40+2733k 0+0io 0pf+0w >> [crees@pegasus]~% time sed -ne "s,^BitchX-[0-9][^|]*[\|]/usr/po,," >> /var/db/pkg/INDEX-9 >> 0.042u 0.000s 0:00.04 100.0% 48+3216k 0+0io 0pf+0w >> >> I've looked at the code, and can't from a brief glance figure out why >> a slightly longer regex makes such a difference-- does it start to >> split it? > > Perhaps second one uses memory cache data? Run both twice and show us the second times. > Nope, same. [crees@pegasus]~% time sed -ne "s,^BitchX-[0-9][^|]*[\|]/usr/por,," /var/db/pkg/INDEX-9 4.703u 0.007s 0:04.85 96.9% 40+2732k 210+0io 0pf+0w [crees@pegasus]~% time sed -ne "s,^BitchX-[0-9][^|]*[\|]/usr/por,," /var/db/pkg/INDEX-9 4.748u 0.007s 0:04.75 99.7% 40+2732k 0+0io 0pf+0w I also get the same on head; [crees@medusa]~% time sed -ne "s,^BitchX-[0-9][^|]*[\|]/usr/por,," /var/db/pkg/INDEX-10 7.813u 0.015s 0:07.96 98.2% 40+183k 0+0io 0pf+0w [crees@medusa]~% time sed -ne "s,^BitchX-[0-9][^|]*[\|]/usr/po,," /var/db/pkg/INDEX-10 0.070u 0.000s 0:00.07 100.0% 45+205k 0+0io 0pf+0w [crees@medusa]~% uname -a FreeBSD medusa 10.0-CURRENT FreeBSD 10.0-CURRENT #0 r250009: Thu May 30 10:11:16 BST 2013 root@medusa:/usr/obj/usr/src/sys/MEDUSA amd64 Chris
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