$DBH->do("BEGIN");  #  explicitly start a new transaction
                    #  this overrides autocommit setting
# ...
$DBH->do("COMMIT");  #end transaction, this is the "expensive part" ti
+mewise
[download]

That way seems to be at least unportable, if not wrong. Why don't you follow the usual DBI procedure documented in DBD::mysql, DBD::MariaDB (with nearly exactly the same wording), Transactions of DBI and in begin_work of DBI? At least, manually issuing BEGIN and COMMIT commands bypasses anything DBI knows about transactions.

Try::Tiny from the example in Transactions of DBI can easily be replaced by eval, and using the standard DBI methods works with all DBI-supported databases capable of transactions, not just with MySQL and MariaDB:

my $dbh=DBI->connect('dbi:...', 'user', 'pass', { RaiseError => 1, Aut
+oCommit => 1, ... });
$dbh->begin_work(); # if this fails, you have tried to nest transactio
+ns.
unless (
    eval {
        change_some_stuff($dbh);
        change_more_stuff($dbh);
        $dbh->commit();
        1;
    }
) {
    warn "Rolling back because: $@";
    eval { $dbh->rollback() };
}
# At this point, either all changes or no changes have happened in the
+ database.
[download]

Alexander