Re: Order of enforcement of CHECK constraints?

On Tue, Mar 24, 2015 at 4:28 PM, Fabrízio de Royes Mello <fabriziomello@gmail.com> wrote:
>
>
>
> 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.
> >
>
> Yeah... you're correct... we need the oid in the index.
>
>
> > 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,


[1] http://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=e5f455f59fed0632371cddacddd79895b148dc07

--
Fabrízio de Royes Mello
Consultoria/Coaching PostgreSQL
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