What is quasing in oracle database

Question

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Answer 1

Quiesce Database mode limits downtime by placing the database in a partially available state while specfic operations are performed using:
ALTER SYSTEM QUIESCE RESTRICTED;
All active non-DBA sessions will proceed until they become inactive. Once all non-DBA sessions are inactive the system is placed in Quiesce mode. As soon as the statement is issued, all attempts to activate an inactive non-DBA session are blocked. Once finished the database can be returned to a fully available state using:
ALTER SYSTEM UNQUIESCE;
The main advantage of this method is that users do not loose their sessions during the process. Also, the shared pool does not have to "warm up" after a shutdown so performance should return to normal instantly. This method is advantageous when performing ALTER TABLE, CREATE OR REPLACE PACKAGE and EXP/IMP operations.
Using database quiesce mode has several restrictions including:
Resource Manager must be switched on as this is the process that restricts the non-DBA sessions.
Quiesce mode is only available for server editions where Resource Manager is available.
When the database is being quiesced, opening a new instance causes a Real Application Clusters environment error.
Database recovery returns the system to a normal state if it was in quiesce mode prior to a crash.
Backups taken while in quiesce mode are considered as normal online backups.
For complete details visit http://download-uk.oracle.com/docs/cd/B28359_01/server.111/b28310/start004.htm