Oracle Data Guard Question

Hi Experts,

I am a newbie to Oracle data guard. For 1 of our cust we have Oracle RAC for prod (2 nodes) and we are setting up a DR site (single node). I was going through the DG documents and to start with i configured physical standby. In our prod site we have 2 diff apps servers accessing the oracle RAC DB and similarly now cust want to set up 2 Apps servers in DR site too. So foll are my concern

with physical standby mode, DR DB is only recieving updates from Prod server (i may be wrong here). But i want to have a full env in DR ste (similar to PROD 2 Apps + Oracl DB), and still DR DB should be in sync with Prod DB. May i know if its possible and if so how could i do it?

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Richard OlutolaConsultantCommented:
Standby is normally in recovery mode, which means it only receives updates from the primary and it is 'not active'.
In this mode you could still have your app servers configured to talk to the standyby instance, however, the app server also will not be active because no users will be pointing to it. Only when the primary is switched to the standby so that the standby becomes the primary, then you point your users to the app servers in the standby location.

This the first situation.
Richard OlutolaConsultantCommented:
The other situation is that you set your standby db to READ ONLY mode. In this case, the standby databse is open for read only activities so that nothing can be written to it. So the app servers in the standby location can have certain users pointing to it for read only activities such as reporting.

There may be some lag in the how current the standby is as a result.

AndersBiroAuthor Commented:

Thanks for the suggstion, so to confirm if i change it to read only mode i can still point my Apps to DR DB? In the event of switching (lik Prim is down and standby become active), do the isntance name of standby be the same or is it accessible as PRIM instance name? Because if the DB name is changed we will have to resintall our application (DR) and i wante dto minimize the down time.

BTW, may i know how can i configure RD in standby and will changing to RO affect the sync in anyway?

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Richard OlutolaConsultantCommented:
Do you not want the standby to be in standby mode? Do you want the 'standby' app servers to be active or do you just want them to be ready for when a switchover/failover occurs?

Normally, the standby will be in recovery mode, best with real-time apply so that is little or no lag. When there is a switchover, then you'll standby application will also be ready to connect since you'll have configured your standby app servers to connect to the standby instance rather than the primary instance.

When your standby is in RO mode, then you cannot have real-time apply, so it cannot be guaranteed that the standby will be in sync with the primary.

Standby mode is normal the normal mode.

Hi Anders,

Now you ask your question about DG, but have you considered any other solutions to your need ?

If I might summarize : you need a new 2 node RAC that would be a perfect copy of your prod 2 node RAC. Now, do you need this new cluster to be open and running as the first (prod) one ?

If yes, you should really go for some other synchronization method that DG (DG only allows 'Active DG' = open read only mode). But there's some other techniques you can use in order to have the 'copy' really open in read-write mode :

- the poor man's tool : streams. It's not suported anymore but still included in oracle releases. Not very user-friendly to configure & maintain.

- the 'oracle recommended' tool : Golden Gate. This is really the Ferrari of the duplication. You can almost have real time duplication and both sides of the copy stream are active. What's more you can go also for syncronization between the 2 sides.

AndersBiroAuthor Commented:
Hi Rolutola,

So just to conlude, the best way is to keep my DR DB in standby and use Real time apply. In the DR Apps side i will point it to DB Standby DB (Not accessing it though) and in case of any crash in Primary, standby will be act as Primary DB and i can start using the DR Apps server. One more doubt,in case of any crash in Primary, wil lstandby DB automaitcally open in Normal mode or do we need to do some switching?

AndersBiroAuthor Commented:
Hi piloute,

Unfortunately our customer policy is to use only DG and has ruled out other options :)
Richard OlutolaConsultantCommented:
That's correct.

You cannot automatically switchover but you can automatically failover. To enable automaic failover, you'll need to configure the dataguard broker, and enable fast start failover.

switchover is reversible and it is used for things like maintenance. but failover is not reversible (without clever tweaking). It is intended for disaster when the primary really crashes and becomes unavailable permanently.

Many shops prefer manual intervention because you don't want an automatic failover to be triggered due to false alarm.


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You do not mention what version of Oracle you are using.

In 11g you can open your physical standby in read-only mode and/or as snapshot database and that way you can test your applications.

Good luck!
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