connection 1: $dbh->oracle;
connection 2: $dbh->sql

use strict;
use warnings;
use DBI;

my $dbh  = DBI->connect( 'DBI:mysql:database=test;host=localhost', 'root', 'pw' );
my $dbh2 = DBI->connect( 'DBI:mysql:database=test;host=localhost', 'root', 'pw' );

DBI->visit_handles(
    sub {
        my ( $driver_handle, $info ) = @_;

        if ($driver_handle->{Type} eq 'db') {
            $driver_handle->disconnect;
        }

        return 1;
    }
);