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Re: serious regex performance degradation after upgrade to perl 5.8 from 5.6

by mce (Curate)
on Jan 21, 2004 at 13:05 UTC ( #322862=note: print w/ replies, xml ) Need Help??


in reply to serious regex performance degradation after upgrade to perl 5.8 from 5.6

Hi All,
I did a quick benchmark test on his code using non threaded 5.8.0 and 5.6.1 and indeed there is a serious performance degradation.

It is the combination of the i and the g regex modifiers that causes the performance issue. If you remove one of them the performance is the sames as in 5.6.1. I did't not dig deeper into this, but there must be an explanation for this.

ps: this is the code I used

#!/usr/local/bin/perl5.8.0 or #!/usr/local/bin/perl5.6.1 use Benchmark; $main::x=join("",(a..z))x100; &timethis(100,\&test); sub test { $main::x =~ s/(.*?)I/$1/isge; }
update On popular demand, here are the benchmark results.
Perl 5.8.0 timethis 1000: 48 wallclock secs (46.76 usr + 0.02 sys = 46.78 CPU) @ + 21.38/s (n=1000) Perl 5.6.1 timethis 1000: 1 wallclock secs ( 0.70 usr + 0.00 sys = 0.70 CPU) @ + 1428.57/s (n=1000)
When debugging with use re "debug", there are some differences (I only post the last few lines) In 5.8.0, it gives
Setting an EVAL scope, savestack=12 24 <opqrstuvwx> <yz> | 1: OPEN1 24 <opqrstuvwx> <yz> | 3: MINMOD 24 <opqrstuvwx> <yz> | 4: STAR Setting an EVAL scope, savestack=12 failed... Setting an EVAL scope, savestack=12 25 <opqrstuvwxy> <z> | 1: OPEN1 25 <opqrstuvwxy> <z> | 3: MINMOD 25 <opqrstuvwxy> <z> | 4: STAR Setting an EVAL scope, savestack=12 failed... Setting an EVAL scope, savestack=12 26 <opqrstuvwxyz> <> | 1: OPEN1 26 <opqrstuvwxyz> <> | 3: MINMOD 26 <opqrstuvwxyz> <> | 4: STAR Setting an EVAL scope, savestack=12 failed... Match failed
whilst in 5.6.1, it returns
SANY can match 1 times out of 1... 23 <opqrstuvw> <xyz> | 6: CLOSE1 23 <opqrstuvw> <xyz> | 8: EXACTF <I> failed... SANY can match 1 times out of 1... 24 <opqrstuvwx> <yz> | 6: CLOSE1 24 <opqrstuvwx> <yz> | 8: EXACTF <I> failed... SANY can match 1 times out of 1... 25 <opqrstuvwxy> <z> | 6: CLOSE1 25 <opqrstuvwxy> <z> | 8: EXACTF <I> failed... SANY can match 1 times out of 1... 26 <opqrstuvwxyz> <> | 6: CLOSE1 26 <opqrstuvwxyz> <> | 8: EXACTF <I> failed... SANY can match 0 times out of 1... failed... Match failed
But, since I am not a regex expert, I have no clue what this means :-)
---------------------------
Dr. Mark Ceulemans
Senior Consultant
BMC, Belgium


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