Обсуждение: constraints names on partitions
Hello I just realized that the current code to assign constraint names to partitions is going against the SQL standard's idea that constraint names must be unique within a schema. When a partition is created, the foreign key gets exactly the same name as the constraint in the parent table. Now maybe you could argue that these constraints should simply be hidden from view, because they are implementation artifacts; and then their names don't matter. But we already expose the partitions themselves as individual tables, so I don't buy this argument. One way to fix this would be to use ChooseConstraintName() for the FK in the partition, as in the attached patch. One caveat with this is that there is no visual clue (in \d <partition>) that distinguishes FKs inherited from the parent rel from ones that have been created in the partition directly. I'm not sure that that's an important issue, though. Another point, maybe more visible, is that if you give an explicit name to the constraint in the parent table, this is completely lost in the partitions -- again with any visual clue to link the two. I'm +0.2 on applying this patch to pg11, but I'd like to hear others' opinions. Thanks -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Вложения
On Fri, Oct 12, 2018 at 12:39 PM Alvaro Herrera <alvherre@2ndquadrant.com> wrote: > I just realized that the current code to assign constraint names to > partitions is going against the SQL standard's idea that constraint > names must be unique within a schema. When a partition is created, the > foreign key gets exactly the same name as the constraint in the parent > table. I guess I don't see the point in trying to do something about this in the partition case but not any other case. The standard may have a rule here, but if we don't follow it in general, what benefit do we get out of trying to sorta follow it in the specific case of partitions with inherited foreign keys? There's probably quite a bit of work to do here to fix this properly - I seem to recall some previous discussion where it didn't seem simple even to ensure that constraint names were unique within a relation in certain corner cases. At any rate, -1 from me for inserting a fix like this between rc1 and final. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
Robert Haas <robertmhaas@gmail.com> writes: > On Fri, Oct 12, 2018 at 12:39 PM Alvaro Herrera > <alvherre@2ndquadrant.com> wrote: >> I just realized that the current code to assign constraint names to >> partitions is going against the SQL standard's idea that constraint >> names must be unique within a schema. When a partition is created, the >> foreign key gets exactly the same name as the constraint in the parent >> table. > I guess I don't see the point in trying to do something about this in > the partition case but not any other case. The standard may have a > rule here, but if we don't follow it in general, what benefit do we > get out of trying to sorta follow it in the specific case of > partitions with inherited foreign keys? There's probably quite a bit > of work to do here to fix this properly - I seem to recall some > previous discussion where it didn't seem simple even to ensure that > constraint names were unique within a relation in certain corner > cases. We moved the goalposts on that recently, see 17b7c302b. Possibly you are recalling the discussion that led up to that. > At any rate, -1 from me for inserting a fix like this between rc1 and final. I agree that this is no time to be messing with it, but I support the general concept of not intentionally violating the SQL spec for automatically-chosen constraint names. We get complaints regularly about the information_schema being inadequate for displaying constraints, and our only defense against that is "don't violate the SQL spec, and you'll be fine using the SQL spec's views". That defense falls down if the system ever automatically chooses duplicate constraint names. I'm not sure that this would be a good thing to change in a point release, either :-(. We might have to just delay the fix to v12. regards, tom lane