Hanging creating of function

Can anyone explain why the first one never completes, but the second one does? (the first one just keeps running, I canceled after ~1 min)
PG version: 8.1 final

-- tblname param has type varchar
create or replace function getcolstring (tblname varchar) returns varchar as $$
declare
table_columns varchar := '';
column_name record;
begin
for column_name in select pga.attname from pg_attribute pga, pg_class pgc
where pga.attrelid = pgc.relfilenode and pgc.relname = tblname and pga.attnum > 0 loop
table_columns := table_columns || column_name.attname || ',';
end loop;

-- chop the last ','
table_columns := substr(table_columns,1,(length(table_columns)-1));

return table_columns;

end;
$$
language plpgsql;

-- tblname param has type text
create or replace function getcolstring (tblname text) returns varchar as $$
declare
table_columns varchar := '';
column_name record;
begin
for column_name in select pga.attname from pg_attribute pga, pg_class pgc
where pga.attrelid = pgc.relfilenode and pgc.relname = tblname and pga.attnum > 0 loop
table_columns := table_columns || column_name.attname || ',';
end loop;

-- chop the last ','
table_columns := substr(table_columns,1,(length(table_columns)-1));

return table_columns;

end;
$$
language plpgsql;

/Mikael