DB link from postgres to Oracle; how to query Dbname.tablename?

Hi all, greetings!
 
Using Oracle Heterogeneous Services (Oracle HS) I have configured/created a DB link from Postgres 9.3 database into Oracle 11gR3 database (with postgres DB user credentials).
 SQL>  create public database link pg_link connect to "postgres" identified by "blahblah"
using 'postgresql';
Since Postgres does not support public synonyms across databases in a cluster, how do I connect to a specific database and query a specific table in this Postgres cluster using the HS DB link?
 
Let's say, if I have 2 Postgres databases named pgdb01 and pgdb02 in the Postgres cluster, using this DB link that I have created in Oracle, how can I query a specific table called table01 from pgdb01 database?
 
Even though the table user_account exists in pgdb01 database, I cannot select from it using the DB link.
 
SQL> select count(*) from mailto:%22user_account%22(at)pg_link;
select count(*) from "user_account"@pg_link;                     *
ERROR at line 1:
ORA-28500: connection from ORACLE to a non-Oracle system returned this message:
ERROR:  relation "user_account" does not exist at character 21;
No query has been executed with that handle {HY000,NativeErr = 1}
ORA-02063: preceding 3 lines from PG_LINK;
 
I tried dbname.tablename syntax, but it didn't work!  BTW, all my tables belong to public schema.
 
Does anyone with DB link expertise try to answer my question?

Thanks,
Bhanu M. Gandikota
Mobile: (415) 420-7740

________________________________
From: Alejandro Brust <alejandrob(at)pasteleros(dot)org(dot)ar>
To: pgsql-admin(at)postgresql(dot)org
Sent: Tuesday, October 1, 2013 12:30 PM
Subject: Re: [ADMIN] PostgreSQL 9.2 - pg_dump out of memory when backuping a database with 300000000 large objects

Did U perform  any vacuumdb / reindexdb before the Pg_dump?

El 01/10/2013 09:49, Magnus Hagander escribió:
> On Tue, Oct 1, 2013 at 11:07 AM, Sergey Klochkov <klochkov(at)iqbuzz(dot)ru> wrote:
>> Hello All,
>>
>> While trying to backup a database of relatively modest size (160 Gb) I ran
>> into the following issue:
>>
>> When I run
>> $ pg_dump -f /path/to/mydb.dmp -C -Z 9 mydb
>>
>> File /path/to/mydb.dmp does not appear (yes, I've checked permissions and so
>> on). pg_dump just begins to consume memory until it eats up all avaliable
>> RAM (96 Gb total on server, >64 Gb available) and is killed by the oom
>> killer.
>>
>> According to pg_stat_activity, pg_dump runs the following query
>>
>> SELECT oid, (SELECT rolname FROM pg_catalog.pg_roles WHERE oid = lomowner)
>> AS rolname, lomacl FROM pg_largeobject_metadata
>>
>> until it is killed.
>>
>> strace shows that pg_dump is constantly reading a large amount of data from
>> a UNIX socket. I suspect that it is the result of the above query.
>>
>> There are >300000000 large objects in the database. Please don't ask me why.
>>
>> I tried googling on this, and found mentions of pg_dump being killed by oom
>> killer, but I failed to find anything related to the huge large objects
>> number.
>>
>> Is there any method of working around this issue?
> I think this problem comes from the fact that pg_dump treats each
> large object as it's own item. See getBlobs() which allocates a
> BlobInfo struct for each LO (and a DumpableObject if there are any,
> but that's just one).
>
> I assume the query (from that file):
> SELECT oid, lomacl FROM pg_largeobject_metadata
>
> returns 300000000 rows, which are then looped over?
>
> I ran into a similar issue a few years ago with a client using a
> 32-bit version of pg_dump, and got it worked around by moving to
> 64-bit. Did unfortunately not have time to look at the underlying
> issue.
>
>