Sort method: external merge

It's kind of lame questions, possibly I'm missing something but my
doubts are as follow:

When planner/executor needs to sort rowsit sorts whole records (i
think so). So in the case when there are many wide columns it takes
quite a lot of memory and sort goes out to the disk because it excess
the work_mem.

Isn't it possible to sort only fields that order matters & some row
identifier/position (don't really know what - oid/ctid are tight to
table but something temporary tight to 'resultset')? It would take
much less memory and could be processed in the work_mem more often.


#  select sum(length(title)) from contacts;
 sum
------
 4225
(1 row)


# explain analyze SELECT * FROM contacts ORDER BY title;
                                                      QUERY PLAN
----------------------------------------------------------------------------------------------------------------------
 Sort  (cost=6303.07..6369.65 rows=26634 width=269) (actual
time=71.945..92.989 rows=26634 loops=1)
   Sort Key: title
   Sort Method:  external sort  Disk: 7368kB
   ->  Seq Scan on contacts  (cost=0.00..1456.34 rows=26634 width=269)
(actual time=0.008..10.995 rows=26634 loops=1)