Active Dataguard (New in 11g)

         
1.Oracle active dataguard enables a physical standby database to be open read -only while Redo Apply is active.
2.In 10g if the standby database opened in read only mode redo application services will not be applied.
3.It is feature of 11g Enterprise Edition and required aditional license.
4.The compatible parameter should be set to 11.0.0 at least to enable this feature.

Using the real time query feature

1.Using the active dataguard feature , the standby database can be opened in the read only mode, while the redo   application is still happening on the standby database.In 10g redo application cannot be stared on the   standby   as long as it is opened as read only mode.
2.In this option no new objects can be created on the standby database.
3.The physical standby database can be opened in read-only mode only if all files were recovered up to the same   SCN.
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How to enable the Real time query via SQL commands?

1. stop redo apply
   SQL> recober managed standby database cancel;

2. Open the database read -only
   sql> alter database open read only;

3. Restart Redo Apply:
   SQL>recover managed standby database disconnect using current logfile;
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Enable Real -Time query via DGMGRL

1. Stop Redo apply 
   DGMGRL> Edit database 'standdb'set state='APPLY=OFF'
2. Using SQL*Plus, open the database read-only:
   SQL> alter database open read only;
3. Restart Redo Apply:
   DGMGRL> edit database 'standdb'set state='apply-on'
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Verification

1.SQL> select open_mode from v$database;
 OPEN_Mode
-------------
Read only with apply

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How to disable the Real Time Query?

1. Shutdown the standby database.
2. Start the standby database in mount stage
3. Restart the media recovery process.
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