o   Switching AutoCommit mode from on to off or vice versa may fail.  You should always check for errors, when changing AutoCommit mode.  The suggested way of doing so is using the DBI flag RaiseError.  If you don't like RaiseError, you have to use code like the following:

$dbh->{'AutoCommit'} = 0;
if ($dbh->{'AutoCommit'}) {
# An error occurred!
}