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Zero Downtime Database Upgrade Using Oracle GoldenGate


This topic is to bring about what and 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:
Heterogeneous replication technology, the term heterogeneous sounds about that it could be 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 archive log) 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 a different platform or moving to a higher version of the 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 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 move from the major bugs
•To move from the panic – 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 the source) needs to be upgraded to 12c (in target).
1.Install and configure GoldenGate in Source

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•Start the capture mechanism of whole database schemas in the source database, i.e. start the first EXTRACT
•This capture mechanism — EXTRACT will capture all the live transactions

2.Setting Local Trail files for the capture mechanism

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•The captured transactions will store in the form of trail files (local trail files).
•The local trail files need to move to the target location so PUMP EXTRACT will help the need.

3.Buildup the target database using expdp/impdp or RMAN
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•To bring the database copy at the target use the Export (expdp) of the whole database with flashback_scn or using SCN based RMAN backup. (choose the backup/restore methods depends on the DB size)
•Once restore, start the DB upgrade in the target. i.e., as per assumption here from 10g to 12c
4.Before the Apply mechanism — Pump Extract
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•Before the Apply mechanism – start the Pump EXTRACT in source
•The pump EXTRACT will take the local trail files, then pumps to target which will create the remote trail files.

5.Start the Apply mechanism — Replicate
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•Apply Mechanism (Replicat) will read the remote trail files and applies the transactions to the target database 12c.
•Now after the zero lag, each live transaction will be applied to the target upgrade database(12c) as in source the EXRACT captured all during the database backup and restore.

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

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•Now the users can be switched to target 12c 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 replicated to catch up before stopping it.

Conclusion:
•After the final step the whole system can be reconfigured for bidirectional replication or can be upgraded to newer version of database following the same steps in reverse, which can be active-active or active to passive.
•If Bi-directional is needed it has to be configured before the user switching activity.
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 GoldenGate 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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