Обсуждение: Trigger vs Rule

Hi all.

There are two tables:

create table device_types (
id int,
name varchar
);
about 1000 rows

create table devices (
id int,
type int REFERENCES device_types(id),
name varchar,
data float
);
about 200000 rows

And about 1000 functions:
create function device_type1(int) returns ..
create function device_type2(int) returns ..
...
create function device_type1000(int) returns ..


What is faster?

One trigger with 1000 ELSE IF
if old.type=1 then
    select device_type1(old.id);
else if old.type=2 then
    select device_type2(old.id);
...
else if old.type=1000 then
    select device_type1000(old.id);
end if;

Or 1000 rules
create rule device_type1 AS ON update to devices
    where old.type=1
    DO select device_type1(old.id);
create rule device_type2 AS ON update to devices
    where old.type=2
    DO select device_type2(old.id);
...
create rule device_type1000 AS ON update to devices
    where old.type=1000
    DO select device_type1000(old.id);

thx.

--
С уважением,
Ключников А.С.

On 2 apr 2006, at 10.31, Ключников А.С. wrote:
> What is faster?
> One trigger with 1000 ELSE IF
> Or 1000 rules

Faster to write and easier to maintain would be to write a trigger
function in pl/pgsql which executes the right function dynamically:

CREATE OR REPLACE FUNCTION exec_device_type() RETURNS trigger AS $$
    EXECUTE "SELECT device_type" || OLD.type || "(OLD.id)";
$$ LANGUAGE plpgsql;

Best would probably be to refactor your device_typeN() functions into
one, that would take N as an argument.


Sincerely,

Niklas Johansson

On 2 apr 2006, at 23.08, Niklas Johansson wrote:

> CREATE OR REPLACE FUNCTION exec_device_type() RETURNS trigger AS $$
>     EXECUTE "SELECT device_type" || OLD.type || "(OLD.id)";
> $$ LANGUAGE plpgsql;


Sorry, I was bitten by the bedbug there: a plpgsql function needs a
little more than that to be functional :)

CREATE OR REPLACE FUNCTION exec_device_type() RETURNS trigger AS $$
BEGIN
    EXECUTE 'SELECT device_type' || OLD.type || '(OLD.id)';
    RETURN NEW/OLD/NULL; -- Depending on your application.
END;
$$ LANGUAGE plpgsql;

But really, you should consider reworking your schema structure.
Having a thousand functions doing almost the same thing is neither
efficient, nor maintainable.



Sincerely,

Niklas Johansson

* Niklas Johansson <spot@tele2.se> [2006-04-03 11:04:25 +0200]:

>
> On 2 apr 2006, at 23.08, Niklas Johansson wrote:
>
> >CREATE OR REPLACE FUNCTION exec_device_type() RETURNS trigger AS $$
> >    EXECUTE "SELECT device_type" || OLD.type || "(OLD.id)";
> >$$ LANGUAGE plpgsql;
>
>
> Sorry, I was bitten by the bedbug there: a plpgsql function needs a
> little more than that to be functional :)
>
> CREATE OR REPLACE FUNCTION exec_device_type() RETURNS trigger AS $$
> BEGIN
>     EXECUTE 'SELECT device_type' || OLD.type || '(OLD.id)';
>     RETURN NEW/OLD/NULL; -- Depending on your application.
> END;
> $$ LANGUAGE plpgsql;
>
> But really, you should consider reworking your schema structure.
> Having a thousand functions doing almost the same thing is neither
> efficient, nor maintainable.
Things are very diferent.
For many types functions not needed, jast update.

I.e. This is a way One trigger with ~1000 else if.
Here was a diametral opinion.
>
>
>
> Sincerely,
>
> Niklas Johansson
>
>
>
>

--
С уважением,
Ключников А.С.
Ведущий инженер ПРП "Аналитприбор"
432030 г.Ульяновск, а/я 3117
тел./факс +7 (8422) 43-44-78
mailto: alexs@analytic.mv.ru