How to pause an Oracle database

Sometimes it is useful to pause a database, and let it finish the running jobs at a later time.
Particularly in environments with shared resources contention may occur. Important databases need to be prioritized while less important ones should be suspended.

For this purpose, you can use the "suspend" command:

alter system suspend;

Alert log:

Mon Oct 05 10:14:49 2015
Suspending database after alter system suspend command

The database_status field in v$instance will reflect the new state of the database:

SQL> select database_status from v$instance;

 DATABASE_STATUS
-----------------

SUSPENDED

When you are ready to resume database activity, issue the following command:

alter system resume;

More info: Oracle Documentation