I can't reproduce this (linux, 5.20.2): 
use Time::HiRes qw(time);

my $n = $ARGV[0];
my %h;
for (1..$n) {
    my $key = sprintf "%06d", $_;
    $h{$key} = 1;
}

my @a;
my $t1 = time;
@a = keys %h;
my $t2 = time;
printf "time = %.3f; secs per 1M keys: %.3f\n",
    ($t2-$t1), ($t2-$t1) / $n * 1_000_000;

[download]
I get the following, which shows that the time per key is nearly constant: 
$ perl foo 1000000
time = 0.400; secs per 1M keys: 0.400
$ perl foo 2000000
time = 0.845; secs per 1M keys: 0.423
$ perl foo 4000000
time = 1.752; secs per 1M keys: 0.438
$ perl foo 8000000
time = 3.792; secs per 1M keys: 0.474
$ perl foo 16000000
time = 9.213; secs per 1M keys: 0.576

[download]

Dave.

In reply to Re: Perl Hash Performance Hits Brick Wall! by dave_the_m
in thread Perl Hash Performance Hits Brick Wall! by BrianP

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.