Assignment beats SELECT INTO

While working on some customer code, I noticed that they have a lot of code that reads like this:

SELECT a,b,c
INTO foo.x, foo,y, foo.z;

I wondered why they were doing it that way, and if it might be easier to read if it was just:

foo := (a,b,c);

Now, these aren't quite the same, especially if foo has more than three fields. But even that could be got around.

But before I tried this out I decided to see how they performed. Here's what happened:

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

That's a very big difference! Direct assignment takes less than 30% of the time that SELECT INTO takes.

I'm going to dig into why this happens, but meanwhile, I have quite a lot of low hanging performance fruit to pick as a result of this.