Re: Largeobject Access Controls (r2460)

Bruce Momjian さんは書きました:
> KaiGai Kohei wrote:
>> Takahiro Itagaki wrote:
>>> KaiGai Kohei  wrote:
>>>
>>>> Tom Lane wrote:
>>>>> Takahiro Itagaki  writes:
>>>>>>    pg_largeobject should not be readable by the
>>>>>>    public, since the catalog contains data in large objects of all users.
>>>>> This is going to be a problem, because it will break applications that
>>>>> expect to be able to read pg_largeobject.  Like, say, pg_dump.
>>>> Is it a right behavior, even if we have permission checks on large objects?
>>> Can we use column-level access control here?
>>>
>>>    REVOKE ALL ON pg_largeobject FROM PUBLIC;
>>> => GRANT SELECT (loid) ON pg_largeobject TO PUBLIC;
>> Indeed, it seems to me reasonable.
>>
>>> We use "SELECT loid FROM pg_largeobject LIMIT 1" in pg_dump. We could
>>> replace pg_largeobject_metadata instead if we try to fix only pg_dump,
>>> but it's no wonder that any other user applications use such queries.
>>> I think to allow reading loid is a balanced solution.
>> Right, I also remind this query has to be fixed up by other reason right now.
>> If all the large objects are empty, this query can return nothing, even if
>> large object entries are in pg_largeobject_metadata.
> 
> "metadata" seems very vague.  Can't we come up with a more descriptive
> name?

What about "property"?
The "metadata" was the suggested name from Robert Haas at the last
commit fest, because we may store any other properties of a large
object in this catalog future.

> Also, how will this affect pg_migrator?  pg_migrator copies
> pg_largeobject and its index from the old to the new server.  Is the
> format inside pg_largeobject changed by this patch?

The format of pg_largeobject was not touched.

> 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?

Thanks,