updatable cursor's test

Hello

I had to update every row of table with an result of external function. It was possibility for testing of some patterns:

postgres=# create table testcursor(i integer primary key, v integer);
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "testcursor_pkey" for table "testcursor"
CREATE TABLE
postgres=# insert into testcursor select i, 0 from generate_series(1,100000) g(i);
INSERT 0 100000
postgres=# analyze testcursor;
ANALYZE

/* external function sample */
create or replace function ext_fce(a integer, b integer)
returns int as $
declare r int;
begin
/* protect section */
begin
  r := b;
exception when others then
  r := null;
end;
return r;
end;
$$ language plpgsql;

1. test - standard update statement

postgres=# update testcursor set v = ext_fce(i, 30);
UPDATE 100000
Time: 4369,246 ms

2. test - update with updateable cursors

create or replace function testc2(_v integer)
returns void as $$
declare
c cursor for select i from testcursor;
_i integer;
begin
open c;
fetch c into _i;
while found loop
  update testcursor set v = ext_fce(_i, _v)
    where current of c;
  fetch c into _i;
end loop;
close c;
end;
$$ language plpgsql;
postgres=# select testc2(20);
testc2
--------

(1 row)

Time: 8434,985 ms

3. test - update with PK

create or replace function testc3(_v integer)
returns void as $$
declare _i integer;
begin
  for _i in select i from testcursor loop
    update testcursor set v = ext_fce(_i,_v) where i = _i;
  end loop;
end;
$$ language plpgsql;
postgres=# select testc3(30);
testc3
--------

(1 row)

Time: 9959,209 ms

Result: Using updateable cursor is about 90% slower than one statement. Usig pk is about 17% slower than updateable cursor. - So updateable cursors has sense and it is well to use it. But every iteration is much slower than one statement's update.