RaiseError on and off

[Kamp, Rolf F, ALSVC]

Hi:
        I see the example in the Perl DBI book dealing with setting
RaiseError OFF when connecting, then turning it ON in a block. I am trying
to do the opposite, with no success.
        I connect to the database with RaiseError ON:
my $dbh = DBI->connect(undef, 'login', 'passwd', {RaiseError=>1}) or die
("Cannot connect to the database " . $DBI::errstr);
        Then I have a bunch of DBI statements that I would like the program
to croak on if an error occurs:

$usg_insert = $dbh->prepare(q{
insert into usage(sid,interval,usage)
values(?, to_date(?, 'MM-DD-YYYY-HH24:MI:SS'), ?)
});
$usg_update = $dbh->prepare(q{
update usage set usage = usage + ?
where sid = ? and interval = to_date(?, 'MM-DD-YYYY-HH24:MI:SS')
});

        Then I have an insert that I would like to catch the error from,
test if the insert failed for a violation of a unique constraint (duplicate
row), then try an update:

if ($usg_select->fetch()) {
  $dbh->{RaiseError} = 0;       # shut error catching OFF (can't get this
right)
  if (!$usg_insert->execute($sid, $startTimeForOracle, $tbytes)) {
    $dbh->{RaiseError} = 1;     # turn error catching back on
    print "INSERT OF USAGE FAILED $DBI::err $DBI::errstr\n";
    if ($DBI::err == 1) {
      if(!$usg_update->execute($tbytes, $sid, $startTimeForOracle)) {
        print "usage update failed $DBI::err $DBI::errstr\n";
      }
    }
  }
  $dbh->{RaiseError} = 1;
}
        I cannot seem to get DBI to allow me to handle the failed insert.
Any ideas or suggestions are greatly appreciated.

- Rolf.