@kazeburo uri.t is failing. I reproduce it locally as well.

@kazeburo the test is failing when you don't have XS of WWW::Form::UrlEncoded.

@miyagawa I found bug in WWW::Form::UrlEncoded::PP. I'm fixing it now.

Hash::MultiValue new and flatten is bit slowly. For reducing HMV cost, this PR caches parameters as arrayref and create HMV instance on demand.
POST/GET data is not so large compared to modern hardware's memory. Even if cache data in two variables, It will not be a problem.

For reducing HMV cost, this PR caches parameters as arrayref and create HMV instance on demand.

Right, but don't we cache H::MV result anyway? Is this to optimize parameters so that we don't calculate H::MV flatten twice? It sounds like a bit micro optimization to me. I get that it might not be that harmful though.

H::MV flatten benchmark. about 3 times faster without twice flatten.
But we already cache H::MV result in parameters, this H::MV->new is called one time per a request. This optimization does not affect the real applications.

Benchmark: running with_flatten, without_flatten for at least 3 CPU seconds...
with_flatten:  3 wallclock secs ( 3.16 usr +  0.00 sys =  3.16 CPU) @ 32478.48/s (n=102632)
without_flatten:  3 wallclock secs ( 3.08 usr +  0.00 sys =  3.08 CPU) @ 91317.21/s (n=281257)
                   Rate    with_flatten without_flatten
with_flatten    32478/s              --            -64%
without_flatten 91317/s            181%              --

script

#!/usr/bin/perl

use strict;
use warnings;
use Benchmark qw/:all/;
use Hash::MultiValue;

my $query_parameter = [ foo => '123', 'bar' => '45678' ];
my $body_parameter = [ b_foo => '123', 'b_bar' => '45678', 'b_baz' => '90123456789'];

cmpthese(timethese(0, {
    with_flatten => sub {
        my $query = Hash::MultiValue->new(@$query_parameter);
        my $body = Hash::MultiValue->new(@$body_parameter);
        my $param = Hash::MultiValue->new(
            $query->flatten,
            $body->flatten
        );
    },
    without_flatten => sub {
        my $param = Hash::MultiValue->new(
            @$query_parameter,
            @$body_parameter
        );
    },
}));

This optimization does not affect the real applications.

Right, then why do we do it? :)

The faster is good if there is no risk or complicated code.

I changed the default buffer length in 06bd1f6