SRL on standby db

Question

Hi all,
I have created a physical standby database following the steps mentioned in Metalink document id [ID 789370.1]. that worked well and logs are being applied when i switch logfile in primary.
But in the document in step 11 it is asking for creating standby redo log groups. I have added 4 srl on standby.
My question is whether it is necessary to add srl on standby database? I have added srl group 4,5,6,7 on primary. when i try to add srl group 4 on stand by it is showing already exist.
Tnx.
Edited by: user4468476 on Oct 4, 2010 10:41 PM

Answer 1

Hi,
From the doc:
3.1.3 Configure a Standby Redo Log
A standby redo log is required for the maximum protection and maximum availability modes and the LGWR ASYNC transport mode is recommended for all databases. Data Guard can recover and apply more redo data from a standby redo log than from archived redo log files alone.
You should plan the standby redo log configuration and create all required log groups and group members when you create the standby database. For increased availability, consider multiplexing the standby redo log files, similar to the way that online redo log files are multiplexed.
Perform the following steps to configure the standby redo log.
Step 1 Ensure log file sizes are identical on the primary and standby databases.
The size of the current standby redo log files must exactly match the size of the current primary database online redo log files. For example, if the primary database uses two online redo log groups whose log files are 200K, then the standby redo log groups should also have log file sizes of 200K.
Step 2 Determine the appropriate number of standby redo log file groups.
Minimally, the configuration should have one more standby redo log file group than the number of online redo log file groups on the primary database. However, the recommended number of standby redo log file groups is dependent on the number of threads on the primary database. Use the following equation to determine an appropriate number of standby redo log file groups:
(maximum number of logfiles for each thread + 1) * maximum number of threads
Using this equation reduces the likelihood that the primary instance's log writer (LGWR) process will be blocked because a standby redo log file cannot be allocated on the standby database. For example, if the primary database has 2 log files for each thread and 2 threads, then 6 standby redo log file groups are needed on the standby database.
Note:
Logical standby databases may require more standby redo log files (or additional ARCn processes) depending on the workload. This is because logical standby databases also write to online redo log files, which take precedence over standby redo log files. Thus, the standby redo log files may not be archived as quickly as the online redo log files. Also, see Section 5.7.3.1.
Step 3 Verify related database parameters and settings.
Verify the values used for the MAXLOGFILES and MAXLOGMEMBERS clauses on the SQL CREATE DATABASE statement will not limit the number of standby redo log file groups and members that you can add. The only way to override the limits specified by the MAXLOGFILES and MAXLOGMEMBERS clauses is to re-create the primary database or control file.
See Oracle Database SQL Reference and your operating system specific Oracle documentation for the default and legal values of the MAXLOGFILES and MAXLOGMEMBERS clauses.
Step 4 Create standby redo log file groups.
To create new standby redo log file groups and members, you must have the ALTER DATABASE system privilege. The standby database begins using the newly created standby redo data the next time there is a log switch on the primary database. Example 3-1 and Example 3-2 show how to create a new standby redo log file group using the ALTER DATABASE statement with variations of the ADD STANDBY LOGFILE GROUP clause.
Example 3-1 Adding a Standby Redo Log File Group to a Specific Thread
The following statement adds a new standby redo log file group to a standby database and assigns it to THREAD 5:
SQL> ALTER DATABASE ADD STANDBY LOGFILE THREAD 5
2> ('/oracle/dbs/log1c.rdo','/oracle/dbs/log2c.rdo') SIZE 500M;
The THREAD clause is required only if you want to add one or more standby redo log file groups to a specific primary database thread. If you do not include the THREAD clause and the configuration uses Real Application Clusters (RAC), Data Guard will automatically assign standby redo log file groups to threads at runtime as they are needed by the various RAC instances.
Example 3-2 Adding a Standby Redo Log File Group to a Specific Group Number
You can also specify a number that identifies the group using the GROUP clause:
SQL> ALTER DATABASE ADD STANDBY LOGFILE GROUP 10
2> ('/oracle/dbs/log1c.rdo','/oracle/dbs/log2c.rdo') SIZE 500M;
Using group numbers can make administering standby redo log file groups easier. However, the group number must be between 1 and the value of the MAXLOGFILES clause. Do not skip log file group numbers (that is, do not number groups 10, 20, 30, and so on), or you will use additional space in the standby database control file.
Note:
Although the standby redo log is only used when the database is running in the standby role, Oracle recommends that you create a standby redo log on the primary database so that the primary database can switch over quickly to the standby role without the need for additional DBA intervention. Consider using Oracle Enterprise Manager to automatically configure standby redo log on both your primary and standby databases.
Step 5 Verify the standby redo log file groups were created.
To verify the standby redo log file groups are created and running correctly, invoke a log switch on the primary database, and then query either the V$STANDBY_LOG view or the V$LOGFILE view on the standby database once it has been created. For example:
SQL> SELECT GROUP#,THREAD#,SEQUENCE#,ARCHIVED,STATUS FROM V$STANDBY_LOG;
GROUP# THREAD# SEQUENCE# ARC STATUS
3 1 16 NO ACTIVE
4 0 0 YES UNASSIGNED
5 0 0 YES UNASSIGNED
And it's better to create both type of redo on each side to prevent the use of failover, switchover.
Verify what you already have on both database.
Loïc