Lesson 2: Cross-Version Migrations with ZDM (11g → 19c)

Ashish Agnihotri

Data Analyst at Exaguru 

Introduction

Many enterprises are still running mission-critical applications on Oracle Database 11g, which is already beyond Premier Support. Migrating these workloads to Oracle 19c, the long-term support release, is a business priority.
The challenge?
  • Version gap (11g → 19c) requires upgrade + migration in a seamless, low-downtime way.
  • Large databases (multi-TB) make downtime windows unacceptable.
This is where Oracle Zero Downtime Migration (ZDM) provides a structured, automated, and safe approach.

ZDM Cross-Version Migration Architecture

  The ZDM architecture can be broken into 3 major layers:  

1.  Source Database (11gR2)

  • On-premises, Exadata, or non-Exadata infrastructure.
  • Database versions supported: 11.2.0.4 (terminal release of 11g).
  • Connectivity to the ZDM host is established via SSH & Oracle Wallets.

2.  ZDM Service Host

  • Orchestrates the migration.
  • Runs pre-checks, prepares target DB, and automates migration workflow.
  • Handles upgrade scripts post-data transport.

3.  Target Database (19c)

  • OCI DB Systems, ExaCC, or ExaCS.
  • Pre-provisioned with Oracle 19c Home.
  • Configured by ZDM with patches, network setup, and compatibility validation.

4.  Data Transport Layer

  • For cross-version migrations, ZDM primarily uses:
    • RMAN (backup/restore with upgrade).
    • Oracle GoldenGate (for logical replication when downtime must be near zero).

Migration Workflow (11g → 19c)

Source (11gR2) → Backup/Standby → Transport Layer → Target (19c) 
1️⃣ Pre-check Phase
  • Validates prerequisites, compatibility, and OS/database environment.
  • Example:
 zdmcli migrate database \    
-sourcedb my11gDB \    
-targetdb my19cCDB \    
-mode rman \    
-precheck

2️⃣ Stage Phase
  • RMAN backups of the 11g database are staged and restored into the 19c environment.
  • Oracle GoldenGate can be optionally configured for continuous replication.

3️⃣ Upgrade Phase
  • After data transfer, ZDM automatically triggers Database Upgrade Assistant (DBUA) non-interactive scripts to upgrade the database dictionary & features.
  • Example of upgrade invocation (internally by ZDM):
 dbupgrade -d /u01/app/oracle/dbhome_19c -c -l /u01/logs/dbupgrade 

4️⃣ Sync Phase (Optional)
  • With GoldenGate, changes on the 11g source are continuously replicated to the 19c target until cutover.

5️⃣ Cutover Phase
  • Final synchronisation completed.
  • ZDM stops 11g DB services and switches traffic to the 19c target.
  • Downtime: usually minutes.

6️⃣ Post-Migration Activities
  • Time zone & dictionary upgrade scripts.
  • Statistics gathering. 
  • Target validation and performance testing.

Internals & Key Components

Component   Role in Cross-Version Migration
RMAN Backup & restore between 11g and 19c homes.
DBUA Scripts   Automates catalog/dictionary upgrade.  
GoldenGate    Handles logical replication for ongoing DML/DDL changes.  
ZDM Pre-check   Ensures compatibility before actual migration.
Cutover Module Manages final switch and downtime window.

Best Practices for 11g → 19c Migration

Run a Pre-check:

  • Ensure source DB is at 11.2.0.4 with the latest PSU.
  • Test upgrade in a sandbox before production.
  • For large databases (>10TB), prefer GoldenGate for near-zero downtime.
  • Always run -precheck to catch OS, storage, or network mismatches.
  • Validate applications in 19c environment post-upgrade (especially deprecated features).

Example ZDM Migration Command

zdmcli migrate database \    
-sourcedb my11gDB \    
-targetdb my19cCDB \    
-mode ogg \    
-sourcenode onprem-host \    
-targetnode oci-host 

  👉 This configures GoldenGate-based cross-version migration with continuous replication.

Closing Thoughts

Migrating from Oracle 11g → 19c is not just a version change—it’s a strategic modernisation step. With ZDM, Oracle offers a fully automated, low-risk, and business continuity-focused migration path.
By leveraging RMAN, DBUA scripts, and Golden Gate, ZDM ensures that enterprises can transition from legacy 11g databases to the stable, supported, and cloud-ready 19c platform—with minimal downtime and maximum confidence.
 Next Step: Lesson 3: Automating ZDM with Ansible & Terraform

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