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среда, 30 июня 2021 г.

Making DBMS_SCHEDULER.CREATE_JOB Transactional

It is known that DBMS_SCHEDULER.CREATE_JOB is non-transactional as opposed to the old DBMS_JOB. There is even an Oracle idea to provide a transactional interface: link. In Oracle 19c DBMS_JOB jobs are actually DBMS_SCHEDULER jobs, and they can be part of a bigger transaction. I was curious how it is done and if I can make it work for DBMS_SCHEDULER jobs.

Here is a test script that I used for this blogpost on 19.9:

SQL> conn / as sysdba
Connected.
SQL>
SQL> alter session set container=pdb;

Session altered.

SQL>
SQL> exec dbms_scheduler.purge_log()

PL/SQL procedure successfully completed.

SQL>
SQL> drop user tc cascade;

User dropped.

SQL>
SQL> grant create job, create session to tc identified by tc;

Grant succeeded.

SQL>
SQL> grant execute on sys.dbms_isched to tc;

Grant succeeded.

Firstly, let us create a traditional DBMS_SCHEDULER job so as to demonstrate that CREATE_JOB is non-transactional. By "non-transactional" here I mean that it does not leave the session in a transaction.

SQL> conn tc/tc@localhost/pdb
Connected.
SQL>
SQL> doc
DOC>################################################################################
DOC>#  Traditional Job
DOC>################################################################################
DOC>#
SQL>
SQL> select dbms_transaction.local_transaction_id from dual;

LOCAL_TRANSACTION_ID
--------------------------------------------------------------------------------


SQL>
SQL> exec dbms_scheduler.create_job( -
>   job_name => 'JOB_NON_TX', -
>   job_type => 'PLSQL_BLOCK', -
>   job_action => 'null;', -
>   enabled    => true)

PL/SQL procedure successfully completed.

SQL>
SQL> select dbms_transaction.local_transaction_id from dual;

LOCAL_TRANSACTION_ID
--------------------------------------------------------------------------------


SQL>
SQL> exec dbms_session.sleep(5)

PL/SQL procedure successfully completed.

SQL>
SQL> col job_name for a10
SQL>
SQL> select job_name, state
  2    from user_scheduler_jobs;

no rows selected

SQL>
SQL> col log_date for a35
SQL> select log_date, job_name, status
  2    from user_scheduler_job_run_details
  3   order by log_date;

LOG_DATE                            JOB_NAME   STATUS
----------------------------------- ---------- ----------
30-JUN-21 12.02.26.780546 PM +01:00 JOB_NON_TX SUCCEEDED

Now, I try the same but I call DBMS_ISCHED.SET_NO_COMMIT_FLAG before calling the CREATE_JOB procedure.

SQL> doc
DOC>################################################################################
DOC>#  Transactional Job
DOC>################################################################################
DOC>#
SQL>
SQL> exec sys.dbms_isched.set_no_commit_flag

PL/SQL procedure successfully completed.

SQL>
SQL> select dbms_transaction.local_transaction_id from dual;

LOCAL_TRANSACTION_ID
--------------------------------------------------------------------------------


SQL>
SQL> exec dbms_scheduler.create_job( -
>   job_name => 'JOB_TX', -
>   job_type => 'PLSQL_BLOCK', -
>   job_action => 'null;', -
>   enabled    => true)

PL/SQL procedure successfully completed.

SQL>
SQL> select dbms_transaction.local_transaction_id from dual;

LOCAL_TRANSACTION_ID
--------------------------------------------------------------------------------
9.23.604

SQL>
SQL> exec dbms_session.sleep(5)

PL/SQL procedure successfully completed.

SQL>
SQL> col job_name for a10
SQL>
SQL> select job_name, state
  2    from user_scheduler_jobs;

JOB_NAME   STATE
---------- ----------
JOB_TX     SCHEDULED

SQL>
SQL> col log_date for a35
SQL> select log_date, job_name, status
  2    from user_scheduler_job_run_details
  3   order by log_date;

LOG_DATE                            JOB_NAME   STATUS
----------------------------------- ---------- ----------
30-JUN-21 12.02.26.780546 PM +01:00 JOB_NON_TX SUCCEEDED

The things are a bit different this time around:

  • DBMS_SCHEDULER.CREATE_JOB left the session in a transaction.
  • The job is not started.
  • It is not demonstrated here, but it is possible to issue rollback and it will remove the job definition.

Such a job gets started as soon as commit is done:

SQL> commit;

Commit complete.

SQL>
SQL> exec dbms_session.sleep(5)

PL/SQL procedure successfully completed.

SQL>
SQL> col job_name for a10
SQL> col state for a10
SQL>
SQL> select job_name, state
  2    from user_scheduler_jobs;

no rows selected

SQL>
SQL> col status for a10
SQL>
SQL> col log_date for a35
SQL> select log_date, job_name, status
  2    from user_scheduler_job_run_details
  3   order by log_date;

LOG_DATE                            JOB_NAME   STATUS
----------------------------------- ---------- ----------
30-JUN-21 12.02.26.780546 PM +01:00 JOB_NON_TX SUCCEEDED
30-JUN-21 12.02.36.835878 PM +01:00 JOB_TX     SUCCEEDED

Conclusion

The post demonstrates that one can utilize undocumented DBMS_ISCHED.SET_NO_COMMIT_FLAG to make DBMS_SCHEDULER.CREATE_JOB transactional. Since the package is undocumented, there is no guarantee that it will keep working in future versions. Hopefully, Oracle will make a transactional interface available someday.

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