my $row = 0;

##</code><code>##

$host_info_REF->{$row}->{$key} = $tmp->{$key};

##</code><code>##

$host_info{$row}{$key} = $tmp->{$key};

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;
use threads::shared;
use Data::Dumper;

my @db_data = (
    { hostname => 'h0', hinfo0 => 'A', hinfo1 => 'B', hinfo2 => 'C' },
    { hostname => 'h1', hinfo0 => 'X', hinfo1 => 'Y', hinfo2 => 'Z' },
);

my %host_info : shared;

my $row = 0;

for my $db_data (@db_data) {
    $host_info{$row} = shared_clone({
        hostname => delete $db_data->{hostname}, host_info => $db_data
    }); 
    ++$row;
}

print Dumper \%host_info;

##</code><code>##

$ pm_thr_compdat.pl
$VAR1 = {
          '1' => {
                   'hostname' => 'h1',
                   'host_info' => {
                                    'hinfo0' => 'X',
                                    'hinfo1' => 'Y',
                                    'hinfo2' => 'Z'
                                  }
                 },
          '0' => {
                   'hostname' => 'h0',
                   'host_info' => {
                                    'hinfo0' => 'A',
                                    'hinfo1' => 'B',
                                    'hinfo2' => 'C'
                                  }
                 }
        };