Master Note: Troubleshooting Oracle Scheduler

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Troubleshooting Steps


Oracle provides a collection of functions and procedures in the DBMS_SCHEDULER package to help simplify management tasks, as well as providing a rich set of functionality for complex scheduling needs.  Collectively, these functions are called the Scheduler, and they are callable from any PL/SQL program.
Prior to Oracle release 10g similar limited functionality was available with DBMS_JOB package.
The Scheduler lets database administrators and application developers control when and where various tasks take place in an enterprise environment. For example, database administrators can schedule and monitor database maintenance jobs such as backups or nightly data warehousing loads and extracts.

Starting from 12c :

The coordinator looks at the root database and all the child PDBs and selects jobs based on the job priority, the job scheduled start time, and the availability of resources to run the job. The latter criterion depends on the consumer group of the job and the resource plan currently in effect. The coordinator makes no attempt to be fair to every PDB. The only way to ensure that jobs from a PDB are not starved is to allocate enough resources to it.

Known Issues Involving Oracle Scheduler

Problems with the Scheduler can be caused by such things as versions, incorrect setups and/or incorrect usage. The steps that follow will help to clarify where the problem might be and provides information that can be collected to help in diagnosing the issue. Please note that for Oracle Jobs, it is important to distinguish between the usage of the conventional Job queue (DBMS_JOB) and the usage of the Scheduler (DBMS_SCHEDULER). DBMS_JOB is mainly used in Oracle version 9i and lower and has been replaced by the Scheduler, which was introduced in Oracle version 10G. This document will focus mainly on Scheduler (DBMS_SCHEDULER) related issues.
Note: It is still possible to use DBMS_JOB in Oracle version 10.

For a thorough list of known issues with the Oracle Scheduler, please refer to:
NOTE 1311355.1 Known Issues And Bugs Using the Scheduler

Diagnosing Scheduler Issues

Firstly, to identify the affected job the following can be used:
<Note 744645.1> How to find the job name if a scheduled job fails with ORA-12012

Building a Testcase

In the area of the Scheduler, a testcase can often help in solving the issue or finding a solution because there are so many ways to build a job structure. Unexpected behavior or errors may be located in the user commands executed by the job and jobs can execute different types of commands, like PLSQL-programs, procedures, external shell scripts and more. Depending on the problem it is useful to test the successful execution of these commands outside the jobs first to confirm if the problem is in fact located in the job usage. Problems occurring after changes in a job setup or with a newly created job setup often benefits showing the behavior using a small testcase where the issue can be reproduced. A guideline for setting up a simple testcase is provided in the following:
Note 807159.1 Sample Code and Select Statements to Build A simple Testcase for Scheduler / Jobs

According to the situation, combine the SQL commands to build as simple a job structure as possible with only the objects that are needed. Replacing large and complex job setups and minimizing the job structure to only the relevant parts of the problem is important to developing a simple testcase where the behavior / problem can be shown in an easy way and can actually help in finding any possible workarounds.

Generic Tracing

When the problem in the job structure cannot be found in an easy manner it is often recommended to activate sql tracing by setting the event 10046. To produce a valuable result, set timed_statistics to true and max_dump_file_size to unlimited before executing the job.
For example:

SQL> alter session set max_dump_file_size=unlimited;
SQL> alter session set timed_statistics = true;
SQL> alter session set events '10046 trace name context forever, level 4';
SQL> BEGIN DBMS_SCHEDULER.run_job (job_name => 'runtest_job',
                                   use_current_session => TRUE);

Please note that by setting the event in a parameter file, each process would have produced a trace. In this case, optimal tracing is set at the session level, where the problem can be reproduced and then tracing disabled. Ensure that only matching traces are uploaded.
Details on how to diagnose the 10046 trace can be found in Note 376442.1 and Note 39817.1

For the Scheduler, additional tracing has been introduced with setting the attribute logging_level for the jobs and using an event to dump further diagnostics for the job coordinator and the job slaves:

Limited Availability Note 461304.1 How to activate tracing for the scheduler[This section is not visible to customers.]

Automatic Scheduling Issues

Common problems with Scheduler are that jobs do not start at the expected time or won't start automatically.
As a first step, confirm that the job runs successfully with an explicit run (dbms_job.run or dbms_scheduler.run_job). This will exclude a configuration problem of the job itself. Once an explicit execution of the affected job is successful, then look at diagnosing the automatic scheduling process:


Until Oracle Database version 11.1 , the setting of the parameter JOB_QUEUE_PROCESSES is not mandatory for the Scheduler. The Job Coordinator starts job slaves on demand, to work on the job queue table. This means setting JOB_QUEUE_PROCESSES to 0 caused DBMS_JOB jobs to not run, but DBMS_SCHEDULER jobs were unaffected and would still run.
Starting with Oracle Database 11g Release 2 (11.2), setting JOB_QUEUE_PROCESSES to 0 causes both DBMS_SCHEDULER and DBMS_JOB jobs not to run. This has been implemented to provide a clean method of stopping all jobs.

Window Issues

Note 742683.1 Scheduled Job That Works Does Not Start In Window

Purging Diagnostics

Note 749440.1 Dbms_scheduler.Purge Not Removing Entries from dba_scheduler_job_run_details  

Schedule Issues

Note 312547.1 Advanced use of DBMS_JOB.SUBMIT 'interval' Parameter
Note 428872.1 Scheduled Jobs Do Not Run After A Re-Start With Repeat_interval => Null.

Issues with Statistic Jobs (10g)

Note 430636.1 GATHER_STATS_JOB Is Not Running
Note 377143.1 How to check what automatic statistics collection is scheduled on 10g
Note 803191.1 Checklist To Diagnose Issues Related To Automatic Run Of Job GATHER_STATS_JOB 

Issues with 11g Autotasks


Helpful Articles / Examples for Scheduler

Note 807159.1 Sample Code and Select Statements to Build A simple Testcase for Scheduler / Jobs
Note 727499.1 Sample how to create a job running chains
Note 1300444.1  How to create a event based chained job
Note 404238.1 How to Disable an Entry from DBMS_SCHEDULER
Note 873691.1 How to Submit a DBMS_SCHEDULER Job to Run Starting with the Nth Day of a Month
Note 461432.1 How To Exclude A Certain Window In A Schedule For A Day Using DBMS_SCHEDULER Package
Note 270256.1 How to create a Job using new 10g Scheduling feature.
Note 1431664.1 - How to build up an event based job - an example
Note 1074141.1 - How to install and setup the Scheduler Agent (schagent) so can run Remote External Jobs

Further Diagnostics

If you were not able to resolve the issue with the details provided in this or referenced documents, please raise a Service Request for further assistance from Oracle Support. Please provide any relevant tracing and/or a testcase as well as the following information:
Collect the information from DBA_SCHEDULER_JOB_LOG

set ver off
set term off
set page 0
set markup html on spool on
spool scheduler.html

--The proceding lines needs to be un commented when executing aganist 12c Database for a CDB (pluggable instance )
--alter session set container='<pdp name>'

alter session set NLS_DATE_FORMAT='DD-MON-RR HH.MI.SS AM'
where rownum<20
order by LOG_DATE
order by LOG_DATE desc
where JOB_NAME in ('')
order by LOG_DATE
show parameter job_queue
spool off
set markup html off spool off

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