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Zero Downtime Database Upgrade Using Oracle Golden Gate


This topic details on how to attain a Zero Downtime Database Upgrade with the technology — Oracle GoldenGate
Introduction to Oracle GoldenGate:

History:
GoldenGate Software was founded in 1995 and was acquired by Oracle in 2009. It was one of the hot topics at the Oracle Open world 2010.

What is Oracle GoldenGate?
It’s a software used for heterogeneous replication, even as a DR solution and most importantly for the Zero Downtime Upgradation/Migration.
Till date Oracle GoldenGate is probably the best replication software which comes in easy to configure and deploy in the large scale environment.

Uses:
In Heterogeneous replication technology, the term heterogeneous could mean the database technology with different versions of database or Operating Systems.
How does Oracle GoldenGate Works:
GoldenGate replication works by capturing the log information (could be redolog or archivelog) and mining that information which will then transformed into INSERT, DELETE, UPDATE, etc and will be applied to the target database.

Features of Oracle GoldenGate:
• Disaster Recovery – Oracle GoldenGate can be used to setup a standby database for DR purpose
• High Availability – Active to Active, Active to passive, synchronizing different two or more systems with the live data and can be used any other right away when one is down.
• Zero Downtime Upgradation/Migration – Moving the database to different platform or moving to higher version of database.
• Other features – Partial table replication, replication of database from higher version to lower or vice versa.
Oracle GoldenGate Supported Topologies:
• Unidirectional — (Standalone Database/E-business Suite to achieve reporting instance)
• Bi-Directional — (Standalone Database/EBS Integration with On Premise Fusion)
• Broadcast — Data Distribution (Standalone Database/E-business Suite)
• Consolidation — Data Warehousing (Standalone Database/E-business Suite)
• Peer to Peer — Load balancing (Standalone Database)
• Cascading — Scalability, Database Tiering (Standalone Database)
Components of Oracle GoldenGate:
Various components available for Oracle GoldenGate, some of the mandatory components are,
• Manager – Controller, allocate port numbers and performs file maintenance.
• Extract (Capture) – it reads data from the data source and writes to a GoldenGate trail file.
• Replicat (Delivery) – it reads trail file data and writes it to the target database.

Zero Downtime Database Upgrade using Oracle GoldenGate:
There are few tasks which have been a very significant challenge in the IT organization, one of which is Upgrading/Migrating a database with zero downtime.
Why Zero Downtime
It’s a known fact, the applications should be available in continuous or nearby-continuous to users who increasingly expect uninterrupted availability of accessing those applications.
At the same time database needs to upgrade, for the following reasons and more.
• To remove major bugs
• To move beyond end of Oracle support period
• To improve the database performance
• To acquire new features.
But here the challenge is, the customer cannot afford to interrupt the business operations. To face this challenge the Oracle has come up with a best practice called “Zero Downtime Database upgrade/migrate using GoldenGate”
Steps to do achieve zero downtime upgrade:
Here let’s assume we have a database 10g (in source) needs to be upgraded to 12c (in target).
1.Install and configure GoldenGate in Source

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2.Setting Local Trail files for the capture mechanism

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•The capture mechanism (EXTRACT) writes the captured transactions on to the local trail files.

3.Buildup the target database using expdp/impdp

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•The Export (expdp) of whole database with flashback_scn

4.Start the Apply mechanism — Pump Extract

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•Start the Apply mechanism – Pump EXTRACT in source and Replicat in Target.
•The pump EXTRACT will capture the local trail files then pumps to Target and locate the remote trail files.

5.Start the Apply mechanism — Replicat

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•Apply Mechanism (Replicat) will read the remote trail files and applies to the target database.
•Each and every live transactions will be applied to the target database.

6.Switch the user to Target Server and Stop capture mechanism

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•Now the users will be switched to another database which does have all the recent transactions.

7.Stop Apply Mechanism

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•Once the users are shifted to the new database, Stop the first Extract, once the extract is stopped, wait for the pump to catch up before stopping it. Once the pump is stopped, wait for the replicat to catch up before stopping it.

Conclusion:
After the final step the source system can be reconfigured for bidirectional replication or can be upgraded to newer version of database following the same steps.

Reference:
1.Zero Downtime Database Upgrade Using Oracle GoldenGate
http://www.oracle.com/technetwork/middleware/goldengate/overview/ggzerodowntimedatabaseupgrades-174928.pdf

2.Oracle GoldenGate zero downtime migration quick start
http://www.oracle.com/us/products/consulting/resource-library/goldengate-zero-downtime-migration-069712.pdf

3.Zero Downtime Migration to Oracle Exadata using Oracle Golden Gate http://www.oracle.com/us/products/middleware/data-integration/migrate-to-exadata-using-goldengate-1424485.pdf

4.Eliminate Database Downtime with Oracle GoldenGate http://www.oracle.com/us/industries/public-sector/eliminate-downtime-goldengate-ds-329464.pdf

Posted on behalf of Hadley Apps DBA Consultant | 4iApps India

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