relcache sometimes initially ignores has_generated_stored

At Wed, 15 Jan 2020 10:11:05 -0800, Andres Freund <andres@anarazel.de> wrote in

Hi,

I think it's probably not relevant, but it confused me for a moment
that RelationBuildTupleDesc() might set constr->has_generated_stored to
true, but then throw away the constraint at the end, because nothing
matches the
/*
* Set up constraint/default info
*/
if (has_not_null || ndef > 0 ||
attrmiss || relation->rd_rel->relchecks)
test, i.e. there are no defaults.

It was as follows before 16828d5c02.

- if (constr->has_not_null || ndef > 0 ||relation->rd_rel->relchecks)

At that time TupleConstr has only members defval, check and
has_not_null other than subsidiary members. The condition apparently
checked all of the members.

Then the commit adds attrmiss to the condition since the corresponding
member to TupleConstr.

+	if (constr->has_not_null || ndef > 0 ||
+		attrmiss || relation->rd_rel->relchecks)

Later fc22b6623b introduced has_generated_stored to TupleConstr but
didn't add the corresponding check.

A quick assert confirms we do indeed pfree() constr in cases where
has_generated_stored == true.

I suspect that's just an intermediate catalog, however, e.g. when
DefineRelation() does
heap_create_with_catalog();
CommandCounterIncrement();
relation_open();
AddRelationNewConstraints().

It does still strike me as not great that we can get a different
relcache entry, even if transient, depending on whether there are other
reasons to create a TupleConstr. Say a NOT NULL column.

I'm inclined to think we should just also check has_generated_stored in
the if quoted above?

I agree to that. We could have a local boolean "has_any_constraint"
to merge them but it would be an overkill.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center

On 2020-01-15 19:11, Andres Freund wrote:

/*
* Set up constraint/default info
*/
if (has_not_null || ndef > 0 ||
attrmiss || relation->rd_rel->relchecks)
test, i.e. there are no defaults.

It does still strike me as not great that we can get a different
relcache entry, even if transient, depending on whether there are other
reasons to create a TupleConstr. Say a NOT NULL column.

I'm inclined to think we should just also check has_generated_stored in
the if quoted above?

Fixed that way.

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

On 2020-02-06 21:29:58 +0100, Peter Eisentraut wrote:

On 2020-01-15 19:11, Andres Freund wrote:

/*
* Set up constraint/default info
*/
if (has_not_null || ndef > 0 ||
attrmiss || relation->rd_rel->relchecks)
test, i.e. there are no defaults.

It does still strike me as not great that we can get a different
relcache entry, even if transient, depending on whether there are other
reasons to create a TupleConstr. Say a NOT NULL column.

I'm inclined to think we should just also check has_generated_stored in
the if quoted above?

Fixed that way.

Thanks.