Remove duplicated row in pg_largeobject_metadata

[Tobias Meyer <t9m@xxxxxxx>]

Well, it seems we have hit a bug in postgresql 10. 

We tried running vacuumlo on a database and it complained at some point with a message

Failed to remove lo 64985186: ERROR:  large object  64985186 does not exist

Removal from database "XXXXX" failed at object 26 of 100.

Yet, object  64985186 is neither in pg_largeobject.loid nor in pg_largeobject_metadata.oid

Researching similar problems did  not yield anything enlightening, except for a comment by Tom Lane that vacuumlo will use an index.

That led be to the assumption an index had gone wrong and I did

REINDEX ( VERBOSE ) TABLE pg_largeobject_metadata;

Which failed with the message 

ERROR:  could not create unique index "pg_largeobject_metadata_oid_index"
DETAIL:  Key (oid)=(665238) is duplicated.

Well, 

select oid,* from pg_largeobject_metadata where oid=665238;

  oid   | lomowner | lomacl
--------+----------+--------
 665238  |    16123 |
(1 row)

That seemed odd, so I decided to do a FULL VACUUM

VACUUM (full, verbose) pg_largeobject_metadata

Now I see

select oid,* from pg_largeobject_metadata where oid=665238;

  oid   | lomowner | lomacl
--------+----------+--------
 665238 |    16123 |
 665238 |    16123 |
(2 rows)

Deleting both would be a no-go, as I cannot INSERT a specific oid to add one back as far as I know.  

So how do I delete only one of the two? 

Luckily this is only a test instance, so I'm not totally freaked out now. 

Note: I randomized the IDs a bit in this post for security reasons, but kept the scale. Please ignore should they be in an unusual range.

Thanks,

Tobias