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  • User AvatarPradip
  • 12 Dec, 2025
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  • 4 Mins Read

Oracle RAC to Single Instance Migration – Practical Steps 

Oracle RAC to Single Instance Migration – Practical Steps & Best Practices

Migrating an Oracle RAC (Real Application Clusters) database to a Single Instance environment is a major architectural shift. It often happens during cloud migration, cost optimization, licensing reduction, or application compatibility requirements.

What is Oracle RAC to Single Instance Migration?

Oracle RAC is a multi-node clustered database that ensures high availability & scalability.
A Single Instance database runs on one server with one instance.

Why migrate from RAC to Single Instance?

  • Licensing cost reduction

  • Moving from on-prem to cloud

  • Application limitations

  • Simpler architecture

  • Lower infrastructure overhead

  • Business requirement for consolidation

Pre-Migration Checklist (Critical Step Before Starting)

Before touching the database, ensure you validate:

1. Validate Oracle Versions

Check if RAC and target SI environment have:

  • Same Oracle version

  • Same PSU/patch level

  • Same character set

  • Same timezone file version

2. Validate Storage & Infrastructure

  • Ensure same or higher storage capacity

  • High IOPS recommended

  • TEMP, REDO, UNDO, DATAFILES sizing

3. Backup Strategy

Take:

  • Full RMAN backup

  • Archivelogs

  • Controlfile backup

  • Password file backup

4. Identify RAC-Specific Features

You must remove/modify:

  • Instance-specific UNDO tablespaces

  • Thread-specific redo logs

  • Services spread across nodes

5. Check Application Downtime

Migration method determines:

  • Full downtime

  • Limited downtime

  • Zero-downtime (GoldenGate)

Migration Methods from Oracle RAC to Single Instance

There are multiple proven approaches:

Method 1: RMAN Backup & Restore (Most Common)

This method includes taking backup from RAC and restoring it on the Single Instance.

Step-by-Step Procedure

  1. Take full RMAN backup on RAC

    RMAN> backup database plus archivelog;

  2. Copy backups to Single Instance server

  3. Create init.ora / spfile

    • Remove RAC parameters (cluster_database, undo tablespaces per instance)

  4. Restore the database

    RMAN> restore controlfile from ... ;
    RMAN> mount;
    RMAN> restore database;
    RMAN> recover database;

  5. Re-create redo logs for single instance

    alter database add logfile ... ;

  6. Open the database

    alter database open resetlogs;

Method 2: Duplicate Database Using RMAN Active Duplicate

This method duplicates the RAC database directly to SI using network copy.

Steps

  1. Ensure tns connectivity

  2. Create pfile

  3. Run RMAN duplicate command:

    RMAN> duplicate target database to 'newdb' from active database nofilenamecheck;

Method 3: Data Pump Export/Import (Cross Platform or Version Change)

Use this when:

  • Moving from Big Endian → Little Endian

  • Changing DB version

  • Consolidation purposes

Steps

  1. Full export:

    expdp system/... full=y directory=DIR dumpfile=full.dmp

  2. Create SI DB

  3. Import:

    impdp system/... full=y directory=DIR dumpfile=full.dmp

H3: Method 4: Oracle GoldenGate (Minimal Downtime)

Best for:

  • Production migration

  • Zero or near-zero downtime

Steps

  1. Enable supplemental logging

  2. Configure extract on RAC

  3. Configure pump & replicat on SI

  4. Perform initial load

  5. Switchover & cutover

  6. Stop extract after lag = 0

RAC-Specific Parameters to Remove or Modify

Critical Parameters

Remove or set:

cluster_database = FALSE
cluster_database_instances = 1
undo_tablespace = UNDOTBS1
instance_number = 1
thread = 1

Redo Thread Cleanup

Drop extra redo log groups for other RAC nodes.

Post Migration Tasks

1. Rebuild Password File

orapwd file=orapwORCL password=oracle

2. Verify Services

Ensure no RAC services are left.

3. Update Listener & TNS

  • Remove SCAN

  • Update host & port details

4. Recompile Invalid Objects

@utlrp.sql

5. Gather Stats

exec dbms_stats.gather_database_stats;

6. Test Application Connectivity

  • Validate sessions

  • Validate reports

  • Validate performance

Common Issues During RAC-to-SI Migration

ORA-01102: Cannot Mount Database

Caused by leftover RAC parameters.

ORA-00119, ORA-00132

Errors due to removed parameters.

Standby File Management Issues

Redo/thread mismatch.

Duplicate Filenames

Use nofilenamecheck during duplication.

Best Practices for a Smooth Migration

  • Test migration in DEV/UAT before PROD

  • Clean RAC parameters beforehand

  • Keep standby database if rollback is needed

  • Use SCAN IP removal checklist

  • Maintain rollback plan & full backups

FAQs – Oracle RAC to Single Instance Migration

Q1: Why would a company move from RAC to Single Instance?

Cost savings, simplicity, cloud migration, or application limitations.

Q2: Does migration require downtime?

Yes—except GoldenGate setup which gives near-zero downtime.

Q3: Which migration method is fastest?

RMAN Duplicate from Active Database.

Q4: Can I convert a RAC database into SI without backup?

Yes, using RMAN active duplicate (no backup needed).

Q5: What happens to cluster-specific objects?

Undo tablespaces, redo threads, RAC parameters must be removed.

Q6: Is performance affected after moving to single instance?

Yes—capacity planning must ensure sufficient CPU, RAM, IOPS.

Q7: Can I migrate RAC PDB/CDB to Single Instance?

Yes, using RMAN duplication or unplug/plug methods.

Conclusion

Migrating an Oracle RAC database to a Single Instance requires proper planning, a clean cutoff strategy, and execution precision. Whether you choose RMAN, Data Pump, or Oracle GoldenGate, understanding the architecture and handling RAC-specific components is key to success.

This guide provides the most practical, step-by-step, and production-ready checklist to make your migration smooth and error-free.

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