Обсуждение: pg_collation_actual_version() ERROR: cache lookup failed for collation 123

As of 257836a75, this returns:

|postgres=# SELECT pg_collation_actual_version(123);
|ERROR:  cache lookup failed for collation 123
|postgres=# \errverbose 
|ERROR:  XX000: cache lookup failed for collation 123
|LOCATION:  get_collation_version_for_oid, pg_locale.c:1754

I'm of the impression that's considered to be a bad behavior for SQL accessible
functions.

In v13, it did the same thing but with different language:

|ts=# SELECT pg_collation_actual_version(123);
|ERROR:  collation with OID 123 does not exist
|ts=# \errverbose 
|ERROR:  42704: collation with OID 123 does not exist
|LOCATION:  pg_collation_actual_version, collationcmds.c:367

-- 
Justin

On Mon, Jan 18, 2021 at 10:59 AM Justin Pryzby > |postgres=# SELECT
pg_collation_actual_version(123);
> |ERROR:  cache lookup failed for collation 123

Yeah, not a great user experience.  Will fix next week; perhaps
get_collation_version_for_oid() needs missing_ok and found flags, or
something like that.

I'm also wondering if it would be better to name that thing with
"current" rather than "actual".

On Mon, Jan 18, 2021 at 11:22 AM Thomas Munro <thomas.munro@gmail.com> wrote:
> On Mon, Jan 18, 2021 at 10:59 AM Justin Pryzby > |postgres=# SELECT
> pg_collation_actual_version(123);
> > |ERROR:  cache lookup failed for collation 123
>
> Yeah, not a great user experience.  Will fix next week; perhaps
> get_collation_version_for_oid() needs missing_ok and found flags, or
> something like that.

Here's a patch that gives:

postgres=# select pg_collation_actual_version(123);
ERROR:  no collation found for OID 123

It's a bit of an odd function, it's user-facing yet deals in OIDs.

> I'm also wondering if it would be better to name that thing with
> "current" rather than "actual".

Here's a patch to do that (note to self: would need a catversion bump).

While tidying up around here, I was dissatisfied with the fact that
there are three completely different ways of excluding "C[.XXX]" and
"POSIX" for three OSes, so here's a patch to merge them.

Also, here's the missing tab completion for CREATE COLLATION, since
it's rare enough to be easy to forget the incantations required.

On Wed, Feb 17, 2021 at 03:08:36PM +1300, Thomas Munro wrote:
>          tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(oid));
>          if (!HeapTupleIsValid(tp))
> +        {
> +            if (found)
> +            {
> +                *found = false;
> +                return NULL;
> +            }
>              elog(ERROR, "cache lookup failed for collation %u", oid);
> +        }
>          collform = (Form_pg_collation) GETSTRUCT(tp);
>          version = get_collation_actual_version(collform->collprovider,
>                                                 NameStr(collform->collcollate));
> +        if (found)
> +            *found = true;
>      }

FWIW, we usually prefer using NULL instead of an error for the result
of a system function if an object cannot be found because it allows
users to not get failures in a middle of a full table scan if things
like an InvalidOid is mixed in the data set.  For example, we do that
in the partition functions, for objectaddress functions, etc.  That
would make this patch set simpler, switching
get_collation_version_for_oid() to just use a missing_ok argument.
And that would be more consistent with the other syscache lookup
functions we have here and there in the tree.
--
Michael

On Wed, Feb 17, 2021 at 8:04 PM Michael Paquier <michael@paquier.xyz> wrote:
> On Wed, Feb 17, 2021 at 03:08:36PM +1300, Thomas Munro wrote:
> >               tp = SearchSysCache1(COLLOID, ObjectIdGetDatum(oid));
> >               if (!HeapTupleIsValid(tp))
> > +             {
> > +                     if (found)
> > +                     {
> > +                             *found = false;
> > +                             return NULL;
> > +                     }
> >                       elog(ERROR, "cache lookup failed for collation %u", oid);
> > +             }
> >               collform = (Form_pg_collation) GETSTRUCT(tp);
> >               version = get_collation_actual_version(collform->collprovider,
> >
NameStr(collform->collcollate));
> > +             if (found)
> > +                     *found = true;
> >       }
>
> FWIW, we usually prefer using NULL instead of an error for the result
> of a system function if an object cannot be found because it allows
> users to not get failures in a middle of a full table scan if things
> like an InvalidOid is mixed in the data set.  For example, we do that
> in the partition functions, for objectaddress functions, etc.  That
> would make this patch set simpler, switching
> get_collation_version_for_oid() to just use a missing_ok argument.
> And that would be more consistent with the other syscache lookup
> functions we have here and there in the tree.

I guess I was trying to preserve a distinction between "unknown OID"
and "this is a collation OID, but I don't have version information for
it" (for example, "C.utf8").  But it hardly matters, and your
suggestion works for me.  Thanks for looking!

On Thu, Feb 18, 2021 at 10:45:53AM +1300, Thomas Munro wrote:
> I guess I was trying to preserve a distinction between "unknown OID"
> and "this is a collation OID, but I don't have version information for
> it" (for example, "C.utf8").  But it hardly matters, and your
> suggestion works for me.  Thanks for looking!

Could you just add a test with pg_collation_current_version(0)?

+       pg_strncasecmp("POSIX.", collcollate, 6) != 0)
I didn't know that "POSIX." was possible.

While on it, I guess that you could add tab completion support for
CREATE COLLATION foo FROM.  And shouldn't CREATE COLLATION complete
with the list of existing collation?
--
Michael