Folks, I thank you for the in sights. I attempted the suggested fixes with the following modified code.

#!/usr/bin/perl -w
use strict;
use DBI;
my $port=3309;
my $host = '127.0.0.1';
my $db = 'udb';
my $username = 'usr';
my $password = 'passwd';
my $dsn = "DBI:mysql:database=$db;host=$host;port=$port";
my $dbh = DBI->connect("$dsn", 
                       "$username",
                       "$password")  
                       or die "Couldn't connect to database: ".DBI->er
+rstr;
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Which is,I think, the suggested TCP socket case using the loopback address for the localhost yet in my hands I still see:

Couldn't connect to database: Access denied for user 'usr'@'localhost'
+ (using password: YES)
[download]

What to try now?