How a Database Is Quiesced

The database administrator uses the ALTER SYSTEM QUIESCE RESTRICTED statement to quiesce the database. Only users SYS and SYSTEM can issue the ALTER SYSTEM QUIESCE RESTRICTED statement. For all instances with the database open, issuing this statement has the following effect:

• Oracle Database instructs the Database Resource Manager in all instances to prevent all inactive sessions (other than SYS and SYSTEM) from becoming active. No user other than SYS and SYSTEM can start a new transaction, a new query, a new fetch, or a new PL/SQL operation.

• Oracle Database waits for all existing transactions in all instances that were initiated by a user other than SYS or SYSTEM to finish (either commit or terminate). Oracle Database also waits for all running queries, fetches, and PL/SQL procedures in all instances that were initiated by users other than SYS or SYSTEM and that are not inside transactions to finish. If a query is carried out by multiple successive OCI fetches, Oracle Database does not wait for all fetches to finish. It waits for the current fetch to finish and then blocks the next fetch. Oracle Database also waits for all sessions (other than those of SYS or SYSTEM) that hold any shared resources (such as enqueues) to release those resources. After all these operations finish, Oracle Database places the database into quiesced state and finishes executing the QUIESCE RESTRICTED statement.

• If an instance is running in shared server mode, Oracle Database instructs the Database Resource Manager to block logins (other than SYS or SYSTEM) on that instance. If an instance is running in non-shared-server mode, Oracle Database does not impose any restrictions on user logins in that instance.

During the quiesced state, you cannot change the Resource Manager plan in any instance.
The ALTER SYSTEM UNQUIESCE statement puts all running instances back into normal mode, so that all blocked actions can proceed. An administrator can determine which sessions are blocking a quiesce from completing by querying the v$blocking_quiesce view.