Most scheduler calls work the same way as they did in non-CDBs, with except for two scheduler global attributes.

To limit job slaves, set the value of the JOB_QUEUE_PROCESSES initialization parameter. In the CDB root, you can set the JOB_QUEUE_PROCESSES initialization parameter to any integer between 0 and 4000 to control the number of slave processes that Scheduler can use at a time. However, inside a PDB container, 0 and 4000 are the only valid values for JOB_QUEUE_PROCESSES:

• 0 (zero) means that no jobs can be run for that PDB.

• 4000 means that jobs can run in that PDB.

For all other global attribute settings, you must be at the PDB level only. For example, if you set the EMAIL_SENDER attribute in the root database, it applies to the jobs that run in the root, not the jobs running in a specific PDB. If you want to pick a new EMAIL_SENDER for a PDB, then you must set the global attribute in that PDB.

The major CDB-related changes are to the job coordinator process.

In a non-CDB, the coordinator looks at all jobs that are ready to run, picks a subset of them to run, and assigns them to job slaves. It also opens and closes windows, which changes the resource plan in effect for the database.

That is essentially what happens inside a CDB except for the following:

• Jobs are selected from all PDBs

  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.

• Windows are open in the PDB and root database levels

  In a non-CDB, only one window can be open at any given time. In a CDB, there are two levels of windows. At the PDB level, windows can be used to set resource plans that allocate resources among consumer groups belonging to that PDB. At the root database level, windows can allocate resources to different PDBs. Therefore, at any time, there can be a window open in the root database and one in each PDB.

• Job slave switches to the specific PDB it belongs to

  The job slaves are essentially the same as in a non-CDB, except that when a slave executes a job, it switches to the PDB that the job belongs to and then executes it. The rest of the code is essentially unchanged.

You can create a job using DBMS_JOB within a PDB, and it will work as before. However, DBMS_JOB has been superseded by DBMS_SCHEDULER.

Support for DBMS_JOB might be removed in future releases of Oracle Database. For this reason, Oracle recommends that you switch from DBMS_JOB to DBMS_SCHEDULER.

For the scheduler, the coordinator now selects jobs to run from every single PDB and not just a single database as was the case before. Also, for the scheduler, the slave will switch into a PDB before executing a job; otherwise, the code is essentially unchanged.

If a PDB is closed with the immediate option, then the coordinator terminates jobs running in the PDB, and the jobs must be recovered before they can run again.

In an Oracle RAC database, the coordinator can, in most cases, recover the jobs on another instance where that PDB is open. So, if the coordinator on the first instance can find another instance where the PDB is still open, it moves the jobs there. In certain cases, moving the jobs to another instance may not be possible. For example, if the PDB in question is not open anywhere else, the jobs cannot be moved. Also, moving a job to another instance is not possible when the job has the INSTANCE_ID attribute set. In this case the job cannot run until the PDB on that instance is open again.

In a non-Oracle RAC case, the question of moving jobs does not arise. Terminated jobs can only be recovered after the PDB is opened again.

Some CDB views are specific to CDBs, whereas others have a CDB-specific column.

• V$ and GV$ views have a CON_ID column that identifies a container whose data is represented by a CDB_* row. In non-CDBs, the CON_ID column is NULL.

• CDB_* views correspond to all Scheduler DBA_* views.

  In a PDB, these views only show objects visible through a corresponding DBA_* view, but all objects are visible in the root. The CDB_* view contains all columns found in a given DBA_* view and the column (CON_ID). In non-CDBs, this column is NULL.