Creating Logical Standby
Reading time: 3 - 5 minutes
Prerequisite
1 : Before setting up a logical standby database, ensure the logical standby database can maintain the data types and tables in your primary database. See Appendix C of the dataguard documentation for a complete list of data type and storage type considerations.
2 : Ensure Table Rows in the Primary Database Can Be Uniquely Identified.
2.1 : Find Tables Without Unique Logical Identifier in the Primary Database.
Use following query to display a list of tables that SQL Apply may not be able to uniquely identify:
SQL> SELECT OWNER, TABLE_NAME FROM DBA_LOGSTDBY_NOT_UNIQUE WHERE (OWNER, TABLE_NAME) NOT IN (SELECT DISTINCT OWNER, TABLE_NAME FROM DBA_LOGSTDBY_UNSUPPORTED) AND BAD_COLUMN = 'Y';
2.2 : If your application ensures the rows in a table are unique, you can create a disabled primary key RELY constraint on the table. Use ALTER TABLE command to add a disabled primary-key RELY constraint.
The following example creates a disabled RELY constraint on a table named mytab, for which rows can be uniquely identified using the id and name columns:
SQL> ALTER TABLE mytab ADD PRIMARY KEY (id, name) RELY DISABLE;
Creating a Logical Standby Database:
Step 1 Create a Physical Standby Database
Create a Physical Standby Database and make sure that there is no error in remote archiving to Standby from Primary Database.
Step 2 Make Sure that Physical Standby is in Sync with Primary Database
Use following query on Standby to check:
SQL>SELECT MAX(AL.SEQUENCE#) "LAST SEQ RECEIVED", MAX(LH.SEQUENCE#) "LAST SEQ APPLIED" FROM V$ARCHIVED_LOG AL, V$LOG_HISTORY LH;
There should not be any difference in Last Seq Received and Last Seq Applied on Physical Standby.
Step 3 Stop Redo Apply on the Physical Standby Database
SQL> ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
Step 4 Set Parameters for Logical Standby in Primary
4.1. Change VALID_FOR in LOG_ARCHIVE_DEST_1 on Primary to (ONLINE_LOGFILES,ALL_ROLES)
LOG_ARCHIVE_DEST_1= 'LOCATION=/u01/arch/online/ VALID_FOR=(ONLINE_LOGFILES,ALL_ROLES) DB_UNIQUE_NAME=prim1'
4.2. Set LOG_ARCHIVE_DEST_3 for logs which will received on Standby from Primary
LOG_ARCHIVE_DEST_3= 'LOCATION=/u01/arch/standby/ VALID_FOR=(STANDBY_LOGFILES,STANDBY_ROLE) DB_UNIQUE_NAME=prim1'
LOG_ARCHIVE_DEST_STATE_3=ENABLE
Note: LOG_ARCHIVE_DEST_3 only takes effect when the primary database is transitioned to the logical standby role.
Step 5 Build a Dictionary in the Redo Data on Primary Database
SQL> EXECUTE DBMS_LOGSTDBY.BUILD;
The DBMS_LOGSTDBY.BUILD procedure waits for all existing transactions to complete. Long-running transactions executed on the primary database will affect the timeliness of this command.
Step 6 Convert to a Logical Standby Database
SQL> ALTER DATABASE RECOVER TO LOGICAL STANDBY <db_name>;
For db_name, specify a database name to identify the new logical standby database. If you are using a spfile for standby, then command will update the db_name parameter otherwise it will issues a message reminding you to set the name of the DB_NAME parameter after shutting down the database.
Step 7 Create a New Password File for Logical Standby Database
$ORAPWD FILE=<filename> PASSWORD=<password> ENTRIES=<max_users>
This step is required in 10.2 only and should not be performed in 11g.
Step 8 Shutdown and Startup Logical Standby Database in Mount Stage
SQL> SHUTDOWN;
SQL> STARTUP MOUNT;
Step 9 Adjust Initialization Parameter on Logical Standby Database
LOG_ARCHIVE_DEST_1= 'LOCATION=/u01/arch/online/ VALID_FOR=(ONLINE_LOGFILES,ALL_ROLES) DB_UNIQUE_NAME=logstd1'
LOG_ARCHIVE_DEST_2= 'SERVICE=prim1 LGWR ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=prim1'
LOG_ARCHIVE_DEST_3= 'LOCATION=/u01/arch/standby/ VALID_FOR=(STANDBY_LOGFILES,STANDBY_ROLE) DB_UNIQUE_NAME=logstd1'
LOG_ARCHIVE_DEST_STATE_1=ENABLE
LOG_ARCHIVE_DEST_STATE_2=ENABLE
LOG_ARCHIVE_DEST_STATE_3=ENABLE
Step 10 Open the Logical Standby Database
SQL> ALTER DATABASE OPEN RESETLOGS;
Step 11 Start Logical Apply on Standby
SQL> ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE;
