In addition to the connection string, the username and the password one can and should configure the database with the DBI specific configuration options (or attributes). These options all go in a HASH reference in the 4th parameter of the DBI connect method.

As the databases and the DBD - Database drivers might all decide arbitrarily on their mode regarding transactions one should always explicitely declare how she wants to operate.

The AutoCommit option.

examples/dbi/attributes.pl
my %attributes = (
    PrintError  => 1,
    RaiseError  => 1,
    AutoCommit  => 1,
    FetchHashKeyName => 'NAME_lc',  #   NAME_uc
    TraceLevel  => 1,  # see Debugging and Trace levels later
);

my $dsn = "dbi:SQLite:dbname=$dbfile";
my $dbh = DBI->connect($dsn, $username, $password, \%attributes);