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What are Enhancements in 9i Data Guard from 8i standby ?

ezhilarasan_1
Occasional Advisor

What are Enhancements in 9i Data Guard from 8i standby ?

Hi,

What are Enhancements in 9i Data Guard from 8i standby ?
Please list out some new features in the Data Guard.

Thanks
Ezhil
4 REPLIES
Sanjay Kumar Suri
Honored Contributor

Re: What are Enhancements in 9i Data Guard from 8i standby ?

The existing (physical) standby product has been renamed as Data Guard in Oracle9i.

Many of the tasks associated with managing a standby database are automated, including initial instantiation, failover, and graceful primary-to-secondary switch-over and switch back.

Administrators can also optionally specify the log apply delay by which each standby site lags the production environment (for increased protection from human errors or corruption), and choose a zero data loss mode in which online redo log data is synchronously sent to the standby site.

http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96653/preface.htm#971610

http://www.oracle-base.com/articles/9i/DataGuard.php

sks
A rigid mind is very sure, but often wrong. A flexible mind is generally unsure, but often right.
ezhilarasan_1
Occasional Advisor

Re: What are Enhancements in 9i Data Guard from 8i standby ?

Hi Sanjay,

Thanks for your reply. I have noted
some enhancements of Data Guard.

BTW, I have one question, anybody
is welcome to reply.
I understand that "Failover" is the
process of activating standby as
primary in case of production down.
But then what is "Switchover",
if it is just switching primary as
standby and standby as primary.
Tell me some senerio or purpose of
doing this, then I will be able to
understand "Switchover".

Thanks
Ezhil
Sanjay Kumar Suri
Honored Contributor

Re: What are Enhancements in 9i Data Guard from 8i standby ?

Hello Ezhil

What is Failover?

1. During a failover operation, a standby database transitions to the primary role and the old primary database is rendered unable to participate in the configuration.

2. Depending on the protection mode under which the old primary database was operating before the failover, there might be little or no data loss during a failover.

3. A failover is typically used only when a primary database becomes unavailable and there is no possibility of restoring it to service within a reasonable amount of time.

4. The specific actions performed during a failover vary based on if a logical or a physical standby database is involved in the failover operation, the state of the configuration at the time of the failover, and on the specific SQL commands used to initiate the failover.

What is Switchover?

1. During a switchover operation, there is no data loss, and the old primary database remains in the configuration as a standby database.

2. A switchover is typically used to reduce primary database downtime during planned outages, such as operating system or hardware upgrades.

3. A switchover operation takes place in two phases. In the first phase, the existing primary database is transitioned to a standby role. In the second phase, a standby database is transitioned to the primary role.

Scenario

9/11 could be a failover situation. Or total destruction of the system, massive power outages can be other scenarios.

Switchover could be for testing purpose, short duration outages (when primary is being repaired), retriving an accident deletion of table from the standby system and other similar situation.

sks
A rigid mind is very sure, but often wrong. A flexible mind is generally unsure, but often right.
Yogeeraj_1
Honored Contributor

Re: What are Enhancements in 9i Data Guard from 8i standby ?

hi Ezhil,

below a great quote from Thomas Kyte on Data Guard:


There are 4 modes to data guard:

a) guaranteed
b) instant
c) rapid
d) delayed (this is the old standby from 8i and before mode)

Data Guard is many things to many people. Data Guard can be "make sure my data persists EVEN if the building in which it was inserted is destroyed". In that case, guaranteed is what you want. Here you prize the data more then anything else in the world. Who might use this? Well -- a bank would. If you transfer $100,000 from account 1 to account 2 and get a confirmation back -- you expect that to be persistant. Well, if it weren't done in more then one location -- SIMULTANEOUSLY -- you would be less assured of that being the case. Banking institutions would use this level of assurance to have the data reside in two geographically disperse locations at all times. They would use this as a replacement for syncronous replication and a two phase commit. Here data guard is providing two things:

a) extremely high levels of data assurance. If it was committed, we got it.
b) a failover site that can be failed over to AS SOON AS A standby site for it is constructed (makes no sense to fail over if your requirement is to have two copies AT ALL TIMES)

So, data guard in this mode provides for exactly what they need.


I believe most situations will permit RAPID mode -- but you must remember that running in rapid mode when the standby is unavailable -- is sort of like running with a failed mirror disk in mirrored pairs. You can still write to the disk but if the disk fails -- you no longer have a mirror do you. It is up to you whether you want to continue or you want to stop.


In short -- data guard has many levels, not just one, and you must pick the appropriate level based on YOUR needs, YOUR situation. If one size fit all -- well, that would be boring ;)



hope this helps too!

regards
Yogeeraj
No person was ever honoured for what he received. Honour has been the reward for what he gave (clavin coolidge)