Re: [BUG] wrong FK constraint name when colliding name on ATTACH

On Fri, Sep 9, 2022 at 4:54 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > Something here doesn't look to be quite right. Starting with this commit CI
> > [1] started to fail on freebsd (stack trace [2]), and in the meson branch I've
> > also seen the crash on windows (CI run[3], stack trace [4]).
>
> The crash seems 100% reproducible if I remove the early-exit optimization
> from GetForeignKeyActionTriggers:

Indeed, reproduced here.

> diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
> index 53b0f3a9c1..112ca77d97 100644
> --- a/src/backend/commands/tablecmds.c
> +++ b/src/backend/commands/tablecmds.c
> @@ -10591,8 +10591,6 @@ GetForeignKeyActionTriggers(Relation trigrel,
> Assert(*updateTriggerOid == InvalidOid);
> *updateTriggerOid = trgform->oid;
> }
> - if (OidIsValid(*deleteTriggerOid) && OidIsValid(*updateTriggerOid))
> - break;
> }
>
> if (!OidIsValid(*deleteTriggerOid))
>
> With that in place, it's probabilistic whether the Asserts notice anything
> wrong, and mostly they don't. But there are multiple matching triggers:
>
> regression=# select oid, tgconstraint, tgrelid,tgconstrrelid, tgtype, tgname from pg_trigger where tgconstraint = 104301;
> oid | tgconstraint | tgrelid | tgconstrrelid | tgtype | tgname
> --------+--------------+---------+---------------+--------+-------------------------------
> 104302 | 104301 | 104294 | 104294 | 9 | RI_ConstraintTrigger_a_104302
> 104303 | 104301 | 104294 | 104294 | 17 | RI_ConstraintTrigger_a_104303
> 104304 | 104301 | 104294 | 104294 | 5 | RI_ConstraintTrigger_c_104304
> 104305 | 104301 | 104294 | 104294 | 17 | RI_ConstraintTrigger_c_104305
> (4 rows)
>
> I suspect that the filter conditions being applied are inadequate
> for the case of a self-referential FK, which this evidently is
> given that tgrelid and tgconstrrelid are equal.

Yes, the loop in GetForeignKeyActionTriggers() needs this:

+ /* Only ever look at "action" triggers on the PK side. */
+ if (RI_FKey_trigger_type(trgform->tgfoid) != RI_TRIGGER_PK)
+ continue;

Likewise, GetForeignKeyActionTriggers() needs this:

+ /* Only ever look at "check" triggers on the FK side. */
+ if (RI_FKey_trigger_type(trgform->tgfoid) != RI_TRIGGER_FK)
+ continue;

We evidently missed this in f4566345cf40b0.

> I'd counsel dropping the early-exit optimization; it doesn't
> save much I expect, and it evidently hides bugs. Or maybe
> make it conditional on !USE_ASSERT_CHECKING.

While neither of these functions are called in hot paths, I am
inclined to keep the early-exit bit in non-assert builds.

Attached a patch.

--
Thanks, Amit Langote
EDB: http://www.enterprisedb.com