On Sun, 11 Dec 2016 05:28:56 -0600 Trevor Cordes <tre...@tecnopolis.ca> wrote:
> On my box the above runs for >2m (never completes before I ^C) on the > version **AFTER** the commits (v2.22). On the test build just *BEFORE* > the commits (2.21.73-8058), it runs in <2s. So for me, I had a working > command (-F -w -f) that used to run quickly, that suddenly became > slow/useless. And none of the suggestions I've read can alleviate the > problem for me, not locale settings, nor anything else. If you can > confirm this is the case on your box, then maybe we can figure out why? Can you re-run with current master, as dfa has been improved frequently? > The main question I think for my case is why is "-F -w -f" switching > modes to the slow DFA at all? AFAIK there's no encoding flaw in the > input, so why is grep even switching modes in this use case? What was > wrong with just using the old mode? From what I've read, people don't > want DFA-mode when using -F and -f. > > Or, there should be an option to grep that we can specify to turn off > this new behavior to get back the old (<2s) performance. > > Thanks! dfa matcher is not always slower than kws matcher. - $ env LC_ALL=C grep -F -w 0 k - $ env LC_ALL=C grep -F -w -f /usr/share/dict/words /dev/null First is faster after the changes, and second is slower after the changes. It's a trade-off. Can you have any idea to select the better matcher for both two cases? If we think simple algorithm as we select kws matcher for grep -F -w -f and select grep dfa matcher for -F -w -e, we will get extreamly different performance for following two cases. - $ env LC_ALL=C grep -F -w -f /usr/share/dict/words /dev/null - $ env LC_ALL=C grep -F -w -e "`cat /usr/share/dict/words`" /dev/null Thanks, Norihiro
