Re: Alter domain type / avoiding table rewrite

On 4/16/19 9:18 AM, Tim Kane wrote:
> Thanks everyone..
>
> It seems that the first step:
>
> old_type --> varchar(9)
>
> still requires a table rewrite, while the reverse direction does not.

Hmm:

CREATE DOMAIN old_type AS varchar(9);

create table rewrite_test (id integer, fld_1 old_type);

insert into rewrite_test values (1, '123456789'), (2, '123');

select ctid from rewrite_test;
ctid
-------
(0,1)
(0,2)

alter table rewrite_test alter COLUMN fld_1 set data type varchar(9);

select ctid from rewrite_test;
ctid
-------
(0,1)
(0,2)

update rewrite_test set fld_1 = '1' where id =2;

select ctid from rewrite_test;

ctid

-------

(0,1)

(0,3)

Where are you seeing the rewrite in your case?

>
>
> I'm curious about the performance implication of domain types, i expect
> that cost is only at insert/update time? I guess we've been wearing that
> cost up until now.
>
> Adrian is correct - the intention for the DOMAIN with CHECK approach was
> to allow flexibility moving forward, as the data set is particularly
> large...
>
> I'm now thinking that since promotion to a larger size is a non-issue,
> and domain type seems to be not quite the panacea I hoped, then the use
> of varchar(n) is perhaps not so terrible!
>
> Thanks for the advice/suggestions/discussion :)
>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com