my $rowcache;
while (my $aref = shift(@$rowcache)
|| shift ( @{$rowcache= $sth->fetchall_arrayref(undef, $max_rows)} )
)

##</code><code>##

       Here’s an example (assumes RaiseError is enabled):

         my $rows = []; # cache for batches of rows
         while( my $row = ( shift(@$rows) || # get row from cache, or reload cache:
                            shift(@{$rows=$sth->fetchall_arrayref(undef,10_000)||[]}) )
         ) {
           ...
         }