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NO. OF REDO LOGS ON PRIMARY AND STANDBY [message #241782]

Wed, 30 May 2007 10:56

jagmohan81@gmail.com
Messages: 6
Registered: May 2007
Location: new jersey

Junior Member

HI EXPERTS

I have a confusion that do you have same number of redo logs on primary and standby .
As i have read on some of the document that you should have one extra redo log group on standby side. Is it required or is helpful for the better working of dataguard.

If we do need to have an extra rodo log , how does it help us .

Can somebody respond me please.

Thanks in advance.

Jagmohan singh

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Re: NO. OF REDO LOGS ON PRIMARY AND STANDBY [message #241798 is a reply to message #241782]

Wed, 30 May 2007 11:41

mlgoins
Messages: 116
Registered: March 2007
Location: Denver, CO

Senior Member

This is covered very well in documentation at http://download-east.oracle.com/docs/cd/B10501_01/server.920/a96653/log_transport.htm#1038266, but this might help:

The Primary and Standby databases have the same number of Online Redo logs. They should have one more Standby Redo Log than Online Redo Log. If you do a switchover (ALTER DATABASE COMMIT TO SWITCHOVER TO PHYSICAL STANDBY), the following recommendation will appear in the Alert Log like this:

...
The primary database controlfile was created using the
'MAXLOGFILES 32' clause.
There is space for up to 28 standby redo logfiles
Use the following SQL commands on the standby database to create
standby redo logfiles that match the primary database:
ALTER DATABASE ADD STANDBY LOGFILE 'srl1.f' SIZE 33554432;
ALTER DATABASE ADD STANDBY LOGFILE 'srl2.f' SIZE 33554432;
ALTER DATABASE ADD STANDBY LOGFILE 'srl3.f' SIZE 33554432;
ALTER DATABASE ADD STANDBY LOGFILE 'srl4.f' SIZE 33554432;
ALTER DATABASE ADD STANDBY LOGFILE 'srl5.f' SIZE 33554432;

Note: this is one more than the number of Online Redo Logs (4).

M

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Re: NO. OF REDO LOGS ON PRIMARY AND STANDBY [message #241800 is a reply to message #241782]

Wed, 30 May 2007 11:43

mlgoins
Messages: 116
Registered: March 2007
Location: Denver, CO

Senior Member

The documentation talks about the benefits of having one (or more than one) Standby Redo log more than Online Redo Logs. Basically, it's to avoid a bottleneck/waiting while Redo is applied. And, you'll find opposing documentation about WHEN the Standby Redo logs are required. What I found from reading around was that they ARE required if you are using LGWR and a Physical Standby Database. Can't imagine what it would look like without them, if it would work at all.

M

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