How To Drop Database Links In Another Schema

How To Drop Database Links In Another Schema

August 22, 2018 4 By dianarobete

You know that you cannot drop a database link in a different schema, by prefixing the database link with the owner’s name.

Which means the following statement will error out:

 drop database link scott.hr_link; 

Have you ever wondered WHY you cannot drop a link in another schema?

Based on Oracle’s documentation, this “rule” is in place because the database link itself can contain the character period in the name.
Therefore the database link hr_link in the scott schema, when referenced as scott.hr_link, is interpreted as the database link with the name of “scott.hr_link”

So, if you need to drop database links in another schema, how do you do it?

There are many ways to do it, I will show you today the one I find the easier. But, before I get to the dropping links, I want you to tell me something!

What is the first thing that comes to your mind, when you hear the word DROP?

When I hear the word drop or delete, the first thing that comes to my mind is how can I rollback, what is my restore plan?
Which automatically creates another question, how do I back up the object or data that I am supposed to drop or delete?

Remember: “A Good DBA always has a rollback plan!

In today’s article, I will not only show you how to drop a database link in another schema, but I will also show you how to back it up and recover in case you need to!

1. Backup Database Links

The best way to backup database links, including the encrypted passwords, is to use the export datapump utility.

First, get a “visual” definition of the database links:

select * from dba_db_links;

Second, run export datapump (expdp) to export the database links. For this exercise, we want to drop the hr_link database link owned by SCOTT:

 
expdp DIRECTORY=DATA_PUMP_DIR 
DUMPFILE=expdp_db_link_HRPRD_scott.dmp 
LOGFILE=expdp_db_link_HRPRD_scott.log 
INCLUDE=DB_LINK SCHEMAS=SCOTT

2. Drop Database Links

Run the following script as the user sys, to drop the database link in another schema. If you have multiple links to drop, run it multiple times, with different values assigned to the variables _owner and _db_link.
The script will create a job in the schema you want to drop the db link. The job will drop the db link. Then, the job is dropped.


define _owner='SCOTT'
define _db_link='HR_LINK'

begin
  dbms_scheduler.create_job(
    job_name=>'&_owner..drop_database_link',
    job_type=>'PLSQL_BLOCK',
    job_action=>'BEGIN execute immediate ''drop database link &_db_link'';END;');
    dbms_scheduler.run_job('&_owner..drop_database_link',false);
    dbms_lock.sleep(3);
    dbms_scheduler.drop_job('&_owner..drop_database_link');
end;
/

After you run the above script, verify database links were dropped, and no longer exist in the database:

select * from dba_db_links; 

3. Create The Rollback Plan

If your backup was to export the database links, the best way to restore them is to import the database links from the dump file generated in Step 1. Make sure you test your backup strategy in the test environment, before you drop the links in production!

 
impdp DIRECTORY=DATA_PUMP_DIR 
DUMPFILE=expdp_db_link_HRPRD_scott.dmp 
LOGFILE=impdp_db_link_HRPRD_scott.log 

Remember before you start dropping or deleting, always think about your recovery strategy!

If you enjoyed this article, and would like to learn more about databases, please sign up below, and you will receive
The Ultimate 3 Step Guide To Find The Root Cause Of The Slow Running SQL!

–Diana