Re: Largeobject Access Controls and pg_migrator

(2009/12/13 11:31), Bruce Momjian wrote:
> Bruce Momjian wrote:
>> KaiGai Kohei wrote:
>>> lo_import() has an another prototype which takes second argument to
>>> specify LOID. Isn't it available to restore a large object with
>>> correct LOID? For example, lo_import('/etc/profile', 1234)
>>
>> I can't use that because the migration has already brought over the
>> pg_largeobject file which has the data.
>>
>>> Or, if you intend to restore metadata in the second lo_import(),
>>> ALTER LAEGE OBJECT and GRANT LARGE OBJECT enable to set up metadata
>>> of a certain large object.
>>
>> Yes, that will work cleanly. The file might be large because I need a
>> GRANT for every large object, but I suppose that is OK.
>
> Uh, I tested pg_migrator and found a problem with this approach:
>
> test=> select loid from pg_largeobject;
> loid
> -------
> 16385
> 16385
> 16386
> (3 rows)
>
> test=> grant all ON LARGE OBJECT 16385 to public;
> ERROR: large object 16385 does not exist
>
> I am wondering if the missing pg_largeobject_metadata row is causing
> this, and again I have no way of creating one with the specified oid.

Can SELECT lo_create(16385); help this situation?

It create an entry into pg_largeobject_metadata, but does not touch
pg_largeobject because it is empty in the initial state.
But, in this case, pg_migrator already bring only data chunks to
pg_largeobject. So, this operation enables to recombine orphan chunks
and a metadata entry.

I'm not clear whether we also check pg_largeobejct has chunks with same
LOID on lo_create(). In the regular operation, it shall never happen.

--
KaiGai Kohei <kaigai(at)kaigai(dot)gr(dot)jp>