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in reply to Re^4: Matching against list of patterns
in thread Matching against list of patterns

Hmm, well, I still don't understand how unwinding array of regexpes can give 10fold improvement.

I re-run your code against a bit different body of data (20 regexp, 5k lines), and results are a bit different: 

Array of regexpes unwinded, with /o:
28.97s user 0.09s system 79% cpu 36.674 total
Array of regexpes unwinded, without /o:
29.95s user 0.04s system 95% cpu 31.481 total

foreach loop, without /o:
2.61s user 0.00s system 100% cpu 2.595 total
foreach loop, with /o:
0.33s user 0.01s system 17% cpu 1.957 total
  • Comment on Re^5: Matching against list of patterns

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Re^6: Matching against list of patterns
by Random_Walk (Prior) on Sep 17, 2004 at 12:00 UTC

    I must say I have been puzzled too..... I have now run a test with an adaption of the short code I posted and got these results (I'll stick my test code at the bottom, its rough as a badgers arse) 

    root@tivpre-master:/home/robinp # ./regexps
with eval "optimisation"
timethis 5000: 56 wallclock secs (52.42 usr +  0.00 sys = 52.42 CPU)
naive
timethis 5000: 16 wallclock secs (15.63 usr +  0.00 sys = 15.63 CPU)

    [download]
    however the other results I posted were for real life code where I do get a magnitude better performance using the eval method. Unfortunately I have written the code for a client and can post neither it or the regex I am using (perhaps I can sanitise a couple of example regex). I suspect that the more complex regex I use and the large number make the saving in re-compilation overcome the cost of running eval. For simpler cases and less regex doing an eval probably costs more than the recompiling overhead.

    Cheers,
    R.

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