AFTER SHUTDOWN Trigger Notes

The AFTER SHUTDOWN trigger in Oracle is a database-level trigger that fires after the database has been shut down. This trigger allows you to execute custom actions after the shutdown process has completed, such as logging the shutdown event, performing post-shutdown clean-up, or triggering external processes.

Unlike the BEFORE SHUTDOWN trigger, which fires before the shutdown process begins, the AFTER SHUTDOWN trigger allows you to perform actions after Oracle has successfully completed its shutdown process.

1. What is an AFTER SHUTDOWN Trigger?

The AFTER SHUTDOWN trigger is executed after the database shutdown is completed. This trigger can be used to perform post-shutdown activities such as logging, cleanup, sending notifications, or performing administrative tasks that are necessary after the database is no longer running.

2. Syntax of the AFTER SHUTDOWN Trigger

The syntax for creating an AFTER SHUTDOWN trigger is as follows:

CREATE OR REPLACE TRIGGER trigger_name

AFTER SHUTDOWN ON DATABASE

DECLARE

   -- Declare variables if needed

BEGIN

   -- Perform actions after shutdown

END;

• trigger_name: The name of the trigger.
• AFTER SHUTDOWN ON DATABASE: Specifies that the trigger fires after the database shutdown has been completed.
• DECLARE: Optional block to declare variables if necessary.
• BEGIN...END: The body of the trigger where the actions to be performed after shutdown are written.

3. Common Use Cases for AFTER SHUTDOWN Triggers

Here are some typical scenarios where AFTER SHUTDOWN triggers can be useful:

a. Logging Shutdown Completion

After the database has shut down, you might want to log the event for auditing or record-keeping purposes. This could include storing a timestamp, shutdown type (normal/abort), or the administrator who performed the shutdown.

Example:

CREATE OR REPLACE TRIGGER log_shutdown_completion

AFTER SHUTDOWN ON DATABASE

DECLARE

BEGIN

   INSERT INTO shutdown_audit (event, shutdown_time, shutdown_type)

   VALUES ('Database Shutdown Completed', SYSDATE, 'Normal');

END;

In this example:

• A record is inserted into the shutdown_audit table indicating the completion of the shutdown event.

b. Cleaning Up Resources

If you need to perform any final clean-up tasks once the database has been shut down (e.g., closing files, stopping background jobs, releasing resources), you can do so in the AFTER SHUTDOWN trigger.

Example:

CREATE OR REPLACE TRIGGER cleanup_after_shutdown

AFTER SHUTDOWN ON DATABASE

DECLARE

BEGIN

   -- Perform clean-up tasks like releasing temporary files or stopping background processes

   EXECUTE IMMEDIATE 'BEGIN cleanup_temp_files; END;';

END;

In this example:

• A stored procedure cleanup_temp_files is called after the database has shut down, which could be used to remove temporary files, stop processes, or perform other resource cleanup.

c. Sending Notifications

You might want to send a notification to an administrator or external system once the database has successfully shut down. This could be done via email, a messaging system, or an external script.

Example:

CREATE OR REPLACE TRIGGER notify_shutdown_completion

AFTER SHUTDOWN ON DATABASE

DECLARE

BEGIN

   -- Send email notification about shutdown completion

   EXECUTE IMMEDIATE 'BEGIN send_email_alert(''admin@example.com'', ''Shutdown Complete'', ''The database has successfully shut down.''); END;';

END;

In this example:

• After shutdown, an email notification is sent to administrators.

4. Behavior and Limitations of AFTER SHUTDOWN Triggers

a. Trigger Firing Conditions

The AFTER SHUTDOWN trigger fires after the shutdown process is completed, regardless of whether the shutdown was done via a SHUTDOWN NORMAL, SHUTDOWN IMMEDIATE, or SHUTDOWN ABORT command. It will not fire if the shutdown is not initiated or completed successfully.

b. No Access to Database

Once the AFTER SHUTDOWN trigger is fired, the database is no longer available for regular operations. This means that you cannot perform any database operations that require accessing database objects (e.g., querying tables, inserting records) once the shutdown is complete.

Therefore, you cannot perform actions that require active database connections after the shutdown process begins.

c. Limited Execution Context

The AFTER SHUTDOWN trigger executes in a limited environment. After shutdown, the database instance is no longer accessible to normal users, and any database operations will be limited to what is possible during the shutdown process. For example:

• You cannot execute SQL queries that access database tables or views.
• The trigger cannot initiate further database connections or sessions.

d. Performance Impact

Since the AFTER SHUTDOWN trigger fires after the database is shut down, there is no direct performance impact on normal database operations. However, if any external operations (like file system cleanup or sending alerts) are being performed, they might take some time.

 

5. Example of a FULL AFTER SHUTDOWN Trigger

Here's a more complete example of an AFTER SHUTDOWN trigger that logs the shutdown event, cleans up temporary files, and sends a notification:

CREATE OR REPLACE TRIGGER after_shutdown_actions

AFTER SHUTDOWN ON DATABASE

DECLARE

BEGIN

   -- Log the completion of the shutdown

   INSERT INTO shutdown_log (event, shutdown_time)

   VALUES ('Database Shutdown Completed', SYSDATE);

  

   -- Clean up temporary files or processes

   EXECUTE IMMEDIATE 'BEGIN cleanup_temp_files; END;';

  

   -- Send an email notification

   EXECUTE IMMEDIATE 'BEGIN send_email_alert(''admin@example.com'', ''Shutdown Notification'', ''The database has successfully shut down.''); END;';

END;

This example performs the following actions:

1. Logs the shutdown event in the shutdown_log table.
2. Calls a custom procedure to clean up temporary files or processes (cleanup_temp_files).
3. Sends an email notification to the administrator about the shutdown completion.

 

6. Considerations and Best Practices

• Limit operations: Since the database is not available after shutdown, ensure that the operations performed in the AFTER SHUTDOWN trigger do not attempt to access the database. This means logging, sending notifications, and invoking external processes are ideal tasks.
• Avoid DDL operations: Like other Oracle triggers, the AFTER SHUTDOWN trigger cannot perform DDL (Data Definition Language) operations, such as creating or dropping tables.
• Minimize execution time: Although the trigger fires after the shutdown is complete, it's still a good practice to ensure that operations in the trigger complete quickly so they do not delay any subsequent administrative activities.
• Error handling: Always include proper error handling within the AFTER SHUTDOWN trigger to ensure that unexpected failures do not affect the shutdown process. For example, you can use an EXCEPTION block to capture and log errors.

Example:

BEGIN

   -- Trigger logic

EXCEPTION

   WHEN OTHERS THEN

      -- Log errors to a file or external system

      INSERT INTO error_log (message, error_time)

      VALUES (SQLERRM, SYSDATE);

END;

 

7. FAQ - AFTER SHUTDOWN Trigger

Q1. Can I perform database operations (such as queries or DML) in an AFTER SHUTDOWN trigger?

No, once the database is shut down, you cannot perform database operations like queries, DML, or DDL. The AFTER SHUTDOWN trigger cannot access database tables or views since the database is no longer running.

Q2. Can I prevent a shutdown from occurring using an AFTER SHUTDOWN trigger?

No, the AFTER SHUTDOWN trigger is executed after the shutdown process has been completed. It cannot stop or prevent the shutdown.

Q3. Is it possible to call external programs from the AFTER SHUTDOWN trigger?

Yes, you can call external programs or scripts from the AFTER SHUTDOWN trigger, but keep in mind that they will run once the database is shut down, and no database operations can occur during this time.

Q4. Can I use the AFTER SHUTDOWN trigger to backup the database?

No, it’s not recommended to use the AFTER SHUTDOWN trigger to perform database backups. Use Oracle’s RMAN or another backup solution to handle backups before shutdown, not within the trigger.

Q5. Can I send notifications to multiple recipients using an AFTER SHUTDOWN trigger?

Yes, you can use the AFTER SHUTDOWN trigger to send notifications to multiple recipients by invoking an external procedure or using built-in functions to send emails or messages.