Steve Bertrand am Dienstag, 10. Januar 2006 18.24:
> Hi all,
Hi Steve
> I've a project on the go, where I must compare a single field of more
> than 3 million database records, then sort them largest to smallest. The
> field will contain up to a 6 digit integer.
(I think you must have a reason not to sort the values while retrieving them
from the database - or is it not a SQL db?)
> Just to ensure the most efficient possible run, I've been doing tests
> with benchmark.
>
> I'll post the relevant code, then the results. What I want to know is
> the cmpthese() results. I *think* that 'b' is much more efficient than
> 'a'. My assumption is that 'b'
you mean: 'a'
> can perform 79531 operations per second,
> where 'b' is only doing 20666. Am I looking at this right? Is the
> Schwartzian Transform really about 300% better than just plain sort?
No, about 300% more _slowly_, since 'a' is doing more per second than 'b'.
This seems also plausible from the fact that the schwarzian transformation in
'b' does a comparison like 'a' does, but does additional work.
> ---- code snip (and yes -w and strict are in effect :) ----
>
> if ($benchTest) {
>
> my $r1 = sub {
> my @unsorted = qw(3 4 9 88 24 1034 28);
>
> my @sorted = sort {$a <=> $b} @unsorted;
> };
>
> my $r2 = sub {
> my @unsorted = qw(3 4 9 88 24 1034 28);
>
> my @sorted =
> map $_->[0],
> sort { $a->[1] <=> $b->[1] }
> map [ $_, $_ ],
> @unsorted;
> };
>
> my $href = { 'a' => $r1, 'b' => $r2, };
> my $result = timethese(-10, $href);
> cmpthese($result);
>
> }
>
> ------------- results -----------
>
> Benchmark: running a, b, each for at least 10 CPU seconds...
> a: 11 wallclock secs (10.59 usr + 0.01 sys = 10.60 CPU) @
> 79531.20/s (n=843155)
> b: 11 wallclock secs (10.44 usr + 0.02 sys = 10.45 CPU) @
> 20665.69/s (n=216021)
>
> Rate b a
> b 20666/s -- -74%
read: b performs 74% compared with a.
> a 79531/s 285% --
hth,
joe
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