use DBI;
use Benchmark;
use strict;
use warnings;

my $dsn = "dbi:mysql:database";
my $dbh = DBI->connect("$dsn",'user','password', {
                        RaiseError => 1,

            }
            );
            
my $statement = qq~SELECT field1,
 field2,
 field3 FROM table~;         

my $key_field = 'table_id';

timethese( 1_000, { 
    array_way => sub { 
          $ary_ref  = $dbh->selectall_arrayref($statement)
          },
    hash_way  => sub { 
          $hash_ref = $dbh->selectall_hashref($statement, $key_field)
          }
                } );