You might consider using separate passes for each string to be found (or a loop over them). The following, with values suited to a large file I had kicking around, ran substantially faster than the alernation regex:
sub two_pass {
my @matched;
open (my $FH, "<$file");
while (my $rec = <$FH>) {
if ( $rec =~ '500_000' ) {
push @matched, $rec;
}
if ( $rec =~ '500_001' ) {
push @matched, $rec;
}
}
print "two pass: " . @matched;
close $FH;
}
Actually, it consistently runs faster than the single string sub, even if I force it to run first, last or in the middle. Whatever position, the timings of all three methods remain very consistent I don't have an explanation for that? I've noticed in the past that with the 5.10+ trie optimisation, alternation regexes are sometimes slower than they are under 5.8. There seems to be a "sweet spot" where it comes into its own: neither too few nor too many alternations and it flies, but below or above those limits and it actually takes longer.
For example, on 5.10, I get these (quite surprising) results consistently:
c:\test>junk31 836952.log
Benchmark:
timing 1 iterations of
AAtwo_pass, BBtwo_string, CCone_string
...
two pass: 10
AAtwo_pass: 6 wallclock secs ( 5.69 usr + 0.78 sys = 6.47 CPU) @ 0
+.15/s (n=1)
(warning: too few iterations for a reliable count)
two string: 10
BBtwo_string: 15 wallclock secs (14.34 usr + 0.73 sys = 15.07 CPU) @
+ 0.07/s (n=1)
(warning: too few iterations for a reliable count)
one string: 7
CCone_string: 15 wallclock secs (14.76 usr + 0.76 sys = 15.52 CPU) @
+ 0.06/s (n=1)
(warning: too few iterations for a reliable count)
But on 5.8 I get these rather more understandable results:
c:\test>\perl32\bin\perl junk31.pl 836952.log
Benchmark:
timing 1 iterations of
AAtwo_pass, BBtwo_string, CCone_string
...
two pass: 10
AAtwo_pass: 8 wallclock secs ( 6.60 usr + 0.69 sys = 7.29 CPU) @ 0
+.14/s (n=1)
(warning: too few iterations for a reliable count)
two string: 10
BBtwo_string: 53 wallclock secs (52.99 usr + 0.70 sys = 53.70 CPU) @
+ 0.02/s (n=1)
(warning: too few iterations for a reliable count)
one string: 7
CCone_string: 7 wallclock secs ( 5.60 usr + 0.92 sys = 6.52 CPU) @
+ 0.15/s (n=1)
(warning: too few iterations for a reliable count)
Maybe it shoudl be possible to disable the trie optimisation for thos cases of alternation where it doesn't benefit.
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
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