Developing and Implementing Applications, concluded - Quiescing and Suspending the Database
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You can temporarily quiesce or suspend the database during your maintenance operations. Using these options allows you to keep the database open during application maintenance, avoiding the time or availability impact associated with database shutdowns.

While the database is quiesced, no new transactions will be permitted by any accounts other than SYS and SYSTEM. New queries or attempted logins will appear to hang until you unquiesce the database. The quiesce feature is useful when performing table maintenance or complicated data maintenance. To use the quiesce feature, you must first enable the Database Resource Manager, as described earlier in this chapter. In addition, the RESOURCE_MANAGEMENT initialization parameter must have been set to TRUE when the database was started, and it must not have been disabled following database startup.

While logged in as SYS or SYSTEM (other SYSDBA privileged accounts cannot execute these commands), quiesce the database:

alter system quiesce restricted;

Any non-DBA sessions logged into the database will continue until their current command completes, at which point they will become inactive. In Real Application Clusters configurations, all instances will be quiesced.

To see if the database is in quiesced state, log in as SYS or SYSTEM and execute the following query:

select Active_State from V$INSTANCE;

The Active_State column value will be either NORMAL (unquiesced), QUIESCING (active non-DBA sessions are still running), or QUIESCED.

To unquiesce the database, use the following command:

alter system unquiesce;

Instead of quiescing the database, you can suspend it. A suspended database performs no I/O to its datafiles and control files, allowing the database to be backed up without I/O interference. To suspend the database, use the following command:

alter system suspend;

NOTE

Do not use this command unless you have put the database in hot backup mode.

Although the alter system suspend command can be executed from any SYSDBA privileged account, you can only resume normal database operations from the SYS and SYSTEM accounts. Use SYS and SYSTEM to avoid potential errors while resuming the database operations. In Real Application Clusters configurations, all instances will be suspended. To see the current status, use the following command:

select Database_Status from V$INSTANCE;

The database will be either SUSPENDED or ACTIVE. To resume the database, log in as SYS or SYSTEM and execute the following command:

alter system resume;

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This article is excerpted from chapter five of the book Oracle Database 10g DBA Handbook, written by Kevin Loney and Bob Bryla (McGraw-Hill/Osborne, 2005; ISBN: 0072231459). Buy this book now.