Re: Order of enforcement of CHECK constraints?

On Mon, Mar 23, 2015 at 12:33 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Fabrízio de Royes Mello <fabriziomello@gmail.com> writes:
> > On Fri, Mar 20, 2015 at 4:37 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >>>> We could fix it by, say, having CheckConstraintFetch() sort the
> >>>> constraints by name after loading them.
>
> > Isn't better do this to read pg_constraint in name order?
>
> > -   conscan = systable_beginscan(conrel, ConstraintRelidIndexId, true,
> > +   conscan = systable_beginscan(conrel, ConstraintNameNspIndexId, true,
>
> Surely not.  That would end up having to read *all* of pg_constraint, not
> only the rows applicable to the current relation.
>

> We could get the index to do the work for us if we changed it from an
> index on conrelid to one on conrelid, conname.  However, seeing that that
> would bloat the index by a factor of sixteen, it hardly sounds like a
> free fix either.
>

But in this way we can save some cicles as Ashutosh complains... or am I missing something?

> I really think that a quick application of qsort is the best-performing
> way to do this.
>

Something like the attached?

With current master:

fabrizio=# create table foo(a integer, b integer);
CREATE TABLE
fabrizio=# alter table foo add constraint aa check(a>0);
ALTER TABLE
fabrizio=# alter table foo add constraint bb check(b>0);
ALTER TABLE
fabrizio=# insert into foo values (0,0);
ERROR:  new row for relation "foo" violates check constraint "bb"
DETAIL:  Failing row contains (0, 0).

With the attached patch:

fabrizio=# create table foo(a integer, b integer);
CREATE TABLE
fabrizio=# alter table foo add constraint aa check(a>0);
ALTER TABLE
fabrizio=# alter table foo add constraint bb check(b>0);
ALTER TABLE
fabrizio=# insert into foo values (0,0);
ERROR:  new row for relation "foo" violates check constraint "aa"
DETAIL:  Failing row contains (0, 0).

Regards,

--
Fabrízio de Royes Mello
Consultoria/Coaching PostgreSQL
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