Re: Largeobject Access Controls and pg_migrator

(2009/12/13 10:39), Bruce Momjian wrote:
> Bruce Momjian wrote:
>> KaiGai Kohei wrote:
>>>> What happens when
>>>> there is no entry in pg_largeobject_metadata for a specific row?
>>>
>>> In this case, these rows become orphan.
>>> So, I think we need to create an empty large object with same LOID on
>>> pg_migrator. It makes an entry on pg_largeobject_metadata without
>>> writing anything to the pg_largeobject.
>>> I guess rest of migrations are not difference. Correct?
>>
>> Agreed.  I have modified pg_migrator with the attached patch which
>> creates a script that adds default permissions for all large object
>> tables.
>
> Oops, seem like I have a problem in getting pg_migrator to populate
> pg_largeobject_metadata:
>
>     test=>  select lo_import('/etc/profile');
>      lo_import
>     -----------
>          16385
>     (1 row)
>     
>     test=>  select lo_import('/etc/profile.env');
>      lo_import
>     -----------
>          16386
>     (1 row)
>     
>     test=>  select oid,* from pg_largeobject_metadata;
>       oid  | lomowner | lomacl
>     -------+----------+--------
>      16385 |       10 |
>      16386 |       10 |
>     (2 rows)

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)

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.

Or, am I missing the problem?

> You might remember that INSERT cannot set the oid of a row, so I don't
> see how pg_migrator can migrate this?  Is there a reason we used 'oid'
> in pg_largeobject_metadata but 'lobj' in pg_largeobject?  Why did't we
> add the lomowner and lomacl columns to pg_largeobject?

A large object consists of multiple tuples within pg_largeobject.
If we added lomowner and lomacl into pg_largeobject, we have to manage
all the pages in a large object to keep consistent state.

-- 
KaiGai Kohei <kaigai@kaigai.gr.jp>