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sub Fetch_w_callback{ # Main DBI retrieval mechanism----
   my ($sql, $callback) = @_;
...
   }
   $sth->finish;
 }

   my $sql= "SELECT blah blah....";
   Fetch_w_callback( "COPY ($sql) TO STDOUT CSV HEADER", # Let pg do c
+sv work 
...
        $state
      );