Question

I have a table in Oracle 11.2 database. I want the database to run an executable file on a remote server if a specific cell in table1 is updated to a value of 1 AND if the number of existing rows in table2 is > 0. I don’t have much experience with what is possible in databases — is the following possible to achieve this?

1. create a job using Oracle Scheduler. The job runs immediately, and is used to run an external executable program on a remote server. The job exists, but is not run until step 5 below (is this possible?).
   http://docs.oracle.com/cd/E11882_01/server.112/e17120/schedadmin001.htm#BAJHIDDC

2. attach a DML trigger to the column of the table that fires on an UPDATE statement.
   http://docs.oracle.com/cd/E11882_01/appdev.112/e25519/triggers.htm#CIHEHBEB

3. have the trigger invoke a PL/SQL subprogram
   http://docs.oracle.com/cd/E11882_01/appdev.112/e25519/triggers.htm#CIHEGACF

4. in the PL/SQL subprogram, perform the following business logic: if a specific cell in table1 equals 1, AND if the number of rows in table 2 is greater than 0, proceed to step 5, otherwise stop (exit, quit).

5. Run the job in step 1

Or, if the job/scheduler is not made to provide this functionality, is there another way to achieve the same thing? That is, have a change in a database table trigger an external job.

UPDATE 1:

I wonder if it’s possible to implement steps 1-5 above by just using Oracle Scheduler with DBMS_SCHEDULER.CREATE_JOB using parameter event_condition?

http://docs.oracle.com/cd/E11882_01/server.112/e25494/scheduse005.htm#CHDIAJEB

Here’s an example from the above link:

BEGIN
DBMS_SCHEDULER.CREATE_JOB (
   job_name            =>  'process_lowinv_j1',
   program_name        =>  'process_lowinv_p1',
   event_condition     =>  'tab.user_data.event_type = ''LOW_INVENTORY''',
   queue_spec          =>  'inv_events_q, inv_agent1',
   enabled             =>  TRUE,
   comments            =>  'Start an inventory replenishment job');
END;

The above code creates a job that starts when an application signals the Scheduler that inventory levels for an item have fallen to a low threshold level.

Could the above code somehow be modified to perform the intended steps? For example, could steps 2-4 above be eliminated by using event_condition here instead? etc. If so, what would it look like, for example, how to set the queue_spec?

Answer 1

Assuming that you install the Oracle Scheduler Agent on the remote server, DBMS_SCHEDULER can run an executable on the remote machine. I would have the DML trigger enqueue a message into an Oracle Advanced Queue (AQ) and use that queue to create an event-based job (DML triggers are not allowed to commit or rollback the transaction but running a DBMS_SCHEDULER job implicitly issues a commit so DML triggers cannot directly run a job). The event-based job and the job that runs the remote executable would be part of a job chain.