Which shows that sub athanasius is up to 5 times faster than sub karlgoethebier. Even easier to see when supplying a positive COUNT value to timethese:
#! perl
use strict;
use warnings;
use Benchmark qw( :hireswallclock cmpthese timethese );
my $string = ".co.uk/Jobs/Company-Sector/C8A6446X4PND86M9WYJ/Tradewind
+/?APath=2.21.0.0.0";
cmpthese(
timethese
(
1_000_000,
{
'karlgoethebier' =>
sub { $string =~ m/.+\/.+\/.+\/.+\/(.+)\/.+/; retu
+rn $1; },
'athanasius' =>
sub { return (split '/', $string)[4] },
}
)
);
Output:
13:09 >perl 390_SoPW.pl
Benchmark: timing 1000000 iterations of athanasius, karlgoethebier...
athanasius: 5.19894 wallclock secs ( 5.15 usr + 0.00 sys = 5.15 CPU)
+ @ 194250.19/s (n=1000000)
karlgoethebier: 20.2485 wallclock secs (20.08 usr + 0.00 sys = 20.08
+CPU) @ 49808.24/s (n=1000000)
Rate karlgoethebier athanasius
karlgoethebier 49808/s -- -74%
athanasius 194250/s 290% --
13:16 >
Not really surprising, since regexen with quantifiers can be expensive:
Avoid regular expressions with many quantifiers.... Such patterns can result in exponentially slow backtracking behavior unless the quantified subpatterns match on their first “pass”.
— The Camel Book, 4th Edition, p. 693.
So, what happens if we limit the backtracking?
#! perl
use strict;
use warnings;
use Benchmark qw( :hireswallclock cmpthese timethese );
my $string = ".co.uk/Jobs/Company-Sector/C8A6446X4PND86M9WYJ/Tradewind
+/?APath=2.21.0.0.0";
cmpthese(
timethese
(
1_000_000,
{
'karlgoethebier' =>
sub { $string =~ m/.+\/.+\/.+\/.+\/(.+)\/.+/; retu
+rn $1; },
'karlgoethebier2' =>
sub { $string =~ m/.+?\/.+?\/.+?\/.+?\/(.+?)\/.+/;
+ return $1; },
'athanasius' =>
sub { return (split '/', $string)[4] },
}
)
);
Result:
13:28 >perl 390_SoPW.pl
Benchmark: timing 1000000 iterations of athanasius, karlgoethebier, ka
+rlgoethebier2...
athanasius: 4.91799 wallclock secs ( 4.88 usr + 0.00 sys = 4.88 CPU)
+ @ 204792.14/s (n=1000000)
karlgoethebier: 20.1721 wallclock secs (20.05 usr + 0.00 sys = 20.05
+CPU) @ 49885.26/s (n=1000000)
karlgoethebier2: 2.55908 wallclock secs ( 2.53 usr + 0.00 sys = 2.53
+ CPU) @ 395569.62/s (n=1000000)
Rate karlgoethebier athanasius karlgoethebie
+r2
karlgoethebier 49885/s -- -76% -8
+7%
athanasius 204792/s 311% -- -4
+8%
karlgoethebier2 395570/s 693% 93%
+--
13:29 >perl 390_SoPW.pl
The regex is now significantly faster than split-with-subscript. Interesting!
Athanasius <°(((>< contra mundum