assignment vs SELECT INTO

[Andrew Dunstan <andrew@xxxxxxxxxxxx>]

I found out today that direct assignment to a composite type is (at 
least in my test) about 70% faster than setting it via SELECT INTO. That 
seems like an enormous difference in speed, which I haven't really been 
able to account for.

Test case:

   andrew=# \d abc
          Table "public.abc"
     Column |  Type   | Modifiers
   --------+---------+-----------
     x      | text    |
     y      | text    |
     z      | integer |
   andrew=# do $x$ declare r abc; begin for i in 1 .. 10000000 loop
   select 'a','b',i into r.x,r.y,r.z; end loop; end; $x$;
   DO
   Time: 63731.434 ms
   andrew=# do $x$ declare r abc; begin for i in 1 .. 10000000 loop r
   := ('a','b',i); end loop; end; $x$;
   DO
   Time: 18744.151 ms


Is it simply because the SELECT is in effect three assignments, so it 
takes nearly 3 times as long?

cheers

andrew


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