Re: [HACKERS] Re: BUG #4689: Expanding the length of a VARCHAR column should not induce a table rewrite

On Thu, Mar 5, 2009 at 3:27 PM, Xuân Baldauf
<xuan--2009(dot)03--submitbug--support--postgresql(dot)org(at)baldauf(dot)org> wrote:
>
>
> Well, while this behaviour is well-known for PostgreSQL, this is actually an
> abuse of syntax. If there are legitimate requirements for rewriting a table,
> then there should be explicit syntax for such a feature, like "ALTER TABLE
> ... REWRITE". Rewriting a table in case of "ALTER TABLE ... TYPE" is, by the
> semantics of that statement, just a side-effect, which may or may not
> happen, depending on how optimized the DBMS is. It is bad design to avoid
> optimization just because an unnecessary side-effect would be optimized
> away.
>

note that this is my opinion and not represent the PGDG (Postgresql
Global Development Group) opinion

> now, back to the problem... is not easier to define a column as TEXT
> and to put a check to constraint the length? if you wanna change the
> constraint that will be almost free
>
> No. Is it possible to change the column type from VARCHAR(5) to TEXT without
> a table-rewrite penalty?
>
>

the idea is to make that change once (and to create new tables just with TEXT)

and then you can make ALTER TABLE ... ADD CHECK (length(column) =
a_value) as many times as you want without the need for a table
rewrite

--
Atentamente,
Jaime Casanova
Soporte y capacitación de PostgreSQL
Asesoría y desarrollo de sistemas
Guayaquil - Ecuador
Cel. +59387171157