Question

Need to select table from Schema2 to Schema1

Asked by: miyahira

Hello experts!

Right now we don't have a DBA, and need to propose a solution to my boss.

We have 02 schemas (Schema_s1 and Schema_s2). Both are in the same server (192.168.1.8). But  they don't "see" each other.

I need that user on schema_s2 will be able only to select Table_S1 of Schema_s1 (no insert nor update nor delete).

1.- What should I check first to ensure that?  Do I have to change tnsnames.ora of server 192.168.1.8?

2.- What would be the best way to allow select from Schema_s2 to Table_S1 of Schema_s1 ? Should I give DBLINK relations between schemas S1 and S2? Is it quite dangerous?


This is my tnsnames.ora of my client PC (the domain name of my organization is xxxx.org):

SCHEMA_S1 =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.8)(PORT = 1521))
    )
    (CONNECT_DATA =
      (SERVICE_NAME = opint.xxxx.org)
    )
  )


SCHEMA_S2 =
 (DESCRIPTION =
   (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.8)(PORT = 1521))
   (CONNECT_DATA =
     (SERVER = DEDICATED)
     (SERVICE_NAME = sircprod)
   )
 )

Thank you!

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Asked On
2009-11-02 at 08:37:20ID24864170
Topic

Oracle Database

Participating Experts
2
Points
500
Comments
8

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Answers

 

by: slightwvPosted on 2009-11-02 at 08:52:48ID: 25721065

First some clarification:  Schemas in Oracle are basically separate users that own objects.

What you are describing are two Instances running on the same machine.

That being said:  Database links are fine as long as your security folks allow them.

I would probably create a seperate user on  Schema_s1, grant select on the table to this new user, then create a synonym.

This way if someone compromises the LINK in some way, they only see that single table.

 

by: miyahiraPosted on 2009-11-02 at 09:35:41ID: 25721497

Yes, Slightwv, you're right about instances. We are used to create one Schema for one User with the same name. That 'd be an instance.

Your suggestion is good. However, I don't know how to create a dblink public

-- On Instance1, I create new_user_s1 only read single table:

CREATE USER NEW_USER_S1 ACCOUNT UNLOCK;
GRANT CONNECT TO NEW_USER_S1;
ALTER USER NEW_USER_S1 DEFAULT ROLE ALL;
GRANT SELECT ON TABLE_S1 TO NEW_USER_S1;

-- Running as NEW_USER_S1 user:

CREATE SYNONYM  Table_S1      FOR  USER_S1.Table_S1;


-- On Instance1, create public dblink
CREATE PUBLIC DATABASE LINK HQ USING 'hq';

-- On Instance2, I can't see dblink 'hq'

SELECT * FROM Table_S1@hq;
--ORA-02019: connection description for remote database not found

 

by: slightwvPosted on 2009-11-02 at 09:41:28ID: 25721565

Don't create a public database link.  Link names should be the same as the tnsnames alias.

You create the link on the instance you wish to use it on.  If you create it on instance1, you won't be able to see it on instance2.

Also, don't grant 'CONNECT'.  They've fixed the issues it later releases but it use to also grant a lot of 'bad' privileges.  Use the new 'CREATE SESSION'.

on instance2:
create database link SCHEMA_S1 connect to new_user_s1 identified by <password> using 'SCHEMA_S1';

The you should be able to do the following from instance2:  select count(*) from table_s1@schema_s1;

 

by: miyahiraPosted on 2009-11-02 at 10:54:58ID: 25722385

Ok. I tried it and worked partially.

On Instance2:
create database link SCHEMA_S1 connect to new_user_s1 identified by <password> using 'SCHEMA_S1';

Database link was created as:  SCHEMA_S1.xxxx.org

However, if I try to test it or to select Table_S1, I got this error:

select count(*) from table_s1@schema_s1;
ORA-12154: TNS:could not resolve the connect identifier specified

Could something be set up to avoid database links? As I said, we've got no DBA at the moment!

 

by: slightwvPosted on 2009-11-02 at 10:57:43ID: 25722415

Stupid question:  Do you need domains?  Check your sqlnet.ora file to see if the domain is getting set.

Try:  select count(*) from table_s1@schema_s1.xxxx.org;

 

by: miyahiraPosted on 2009-11-02 at 11:19:42ID: 25722659

Of course I tried both ways:

select count(*) from table_s1@schema_s1.xxxx.org;

select count(*) from table_s1@schema_s1;

Error was the same: ORA-12154

I read in other forums that perhaps I should look the names of instances at tnsnames.ora of db server 192.18.1.8 and not my tnsnames.ora!

 

by: slightwvPosted on 2009-11-02 at 11:27:47ID: 25722748

Correct.  It's the tnsnames file on the server where the link is created.  Sorry for the confusion on my part.

 

by: markgeerPosted on 2009-11-02 at 11:58:33ID: 25723086

You posted a tnsnames.ora file from a client PC, but the one that is used by a database link is the tnsnames.ora file on the Oracle server.  Do you have two separate Oracle_homes (installs of the Oracle server executable software) for these two instances, or do they both run from a single Oracle_home?  Either way is possible, and they both have advantages and disadvantages.  You need the tnsnames.ora file for your instance 2 (schema_2) to have an entry in it that points to instance 1 (schema_1).  The TNS error you received indicates that this entry is missing.

Try connecting in SQL*Plus on the server from the Oracle_home that shema_2 runs from to schema_1.  If that works, then you should be able to set up a database link in schema_2 (instance 2) that also connects to schema_1 (instance_1).

I'm curious, which server O/S is this?  Is this a 32-bit or 64-bit server?  How much RAM does the server have?  What is the size of the two Oracle SGAs?  No, the answers to these won't help us solve the database link problem, but you could have other problems if you have two instances on a single server and if the server O/S and/or the Oracle initialzation parameters are not optimized for this.

Also note that even if the server O/S and the two Oracle initialzation parameters are optimized for your server hadrware  and your application, queries that include a database link will often be 100 to 1000 (or more) times slowere than queries that can be resolved within a single instance of Oracle.  Depending on the sizes of your two instances, the number of user connections, the amount of RAM in the server, and other factors, using a database link may or may not introduce a significant performance penalty.

20120131-EE-VQP-002

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