Oracle to SAP HANA database migration

 Migrating an SAP database from Oracle to SAP HANA is a significant undertaking that goes beyond a simple "lift and shift." It involves a fundamental change in the underlying database technology, impacting performance, analytics capabilities, and the overall SAP landscape. This migration is typically a prerequisite for moving to SAP S/4HANA or leveraging the full power of in-memory computing for existing SAP ECC or BW systems.

Let's break down the process in detail, highlighting critical aspects from a Basis perspective.

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Understanding the Migration Context

Before diving into the steps, it's crucial to understand why this migration happens and the different scenarios:

• SAP ECC on Oracle to SAP ECC on HANA: This is a pure database migration. The SAP application layer (ECC) remains the same, but its database changes from Oracle to HANA. This immediately brings performance benefits to the existing ECC system.
• SAP BW on Oracle to SAP BW on HANA: Similar to ECC, this is a database migration for the SAP Business Warehouse system, enabling in-memory analytics.
• SAP ECC on Oracle to SAP S/4HANA (Greenfield/Brownfield): This is the most common scenario now. It's not just a database migration but a full "conversion" or "new implementation" to SAP's next-generation ERP.
  • Brownfield (System Conversion): Migrating the existing SAP ECC system and its data directly to S/4HANA.¹ The database migration is an integral part of this conversion process, often handled by the Software Update Manager with Database Migration Option (SUM DMO).
  • Greenfield (New Implementation): A fresh installation of S/4HANA, followed by selective data migration from the old ECC system.² The Oracle to HANA migration might happen as a separate initial step for the old ECC system before data is moved to the new S/4HANA, or data is extracted directly from Oracle and loaded into the new S/4HANA on HANA.

This explanation will primarily focus on the Database Migration Option (DMO) of SUM for a brownfield-like scenario, as it's the most common and robust approach for converting an existing SAP system's database while keeping the application layer intact or upgrading it.

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Detailed Phases of SAP Database Migration (Oracle to HANA using SUM DMO)

The migration process is typically divided into several phases:

Phase 1: Planning and Preparation (Crucial)

1. Project Scoping & Strategy:
   • Define Objectives: What are the key drivers? Performance? S/4HANA readiness? Analytics?
   • Migration Scope: Which SAP systems? What downtime is acceptable?
   • Migration Approach: DMO of SUM is often preferred for its one-step nature (upgrade + migration).³
   • Resource Planning: Identify required skills (Basis, HANA Admin, Functional, Developers, Testing).
2. SAP Readiness Checks & Analysis:
   • SAP Readiness Check for S/4HANA (if applicable): This tool analyzes the current ECC system for compatibility with S/4HANA, including custom code, interfaces, and business functions.
   • Simplification List: Understand changes in data models and functionalities in S/4HANA.
   • Pre-checks & Sizing:
     • SAP Business Suite on HANA Sizing Report (/SDF/HANA_SIZING): Run this report on the Oracle system to get an accurate estimate of the HANA memory footprint required. This is critical for hardware procurement.
     • HANA Hardware Sizing: Determine the CPU, memory, and storage requirements for the new HANA database server based on the sizing report. Consider scale-up (single large server) vs. scale-out (multiple smaller servers for larger data volumes/BW).
     • Disk Sizing: Plan for data, log, and backup volumes for HANA.
   • Unicode Conversion Check: SAP HANA only supports Unicode. If the source Oracle system is non-Unicode, a Unicode conversion must be performed as part of the migration or as a preceding step.
   • Custom Code Analysis:
     • ABAP Test Cockpit (ATC) / Code Inspector: Analyze custom ABAP code for HANA compatibility issues (e.g., native SQL, secondary index usage, table joins).⁴ Custom code needs to be adapted for HANA's columnar store and in-memory paradigm.
     • SQL Migration Tools: For non-ABAP applications, specific tools might be needed to convert Oracle-specific SQL to HANA SQL.
3. Data Volume Management (DVM):
   • Data Archiving & Deletion: This is a highly recommended precursor. Reduce the database size by archiving or deleting old, irrelevant, or duplicate data from the Oracle system. A smaller source database means faster migration, smaller HANA footprint, and better performance.
   • Housekeeping: Clean up old logs, temporary data, and system-level junk.
4. Hardware & Software Procurement:
   • HANA Server: Procure or provision the certified SAP HANA server (Appliance or TDI - Tailored Data Center Integration).
   • OS Installation & Configuration: Install and configure the certified OS (SLES or RHEL) on the HANA server.
   • Network Setup: Ensure high-speed, low-latency network connectivity between the new HANA server and the SAP application servers.
   • Storage: Configure high-performance storage for HANA data and log volumes.
5. Licensing: Obtain necessary SAP HANA licenses.
6. Team Training: Ensure Basis, functional, and development teams are trained on SAP HANA concepts and tools.

Phase 2: Pre-Migration Execution

1. Source System Preparation:
   • Database Consistency Check: Ensure the Oracle database is consistent and healthy. Run DB checks, verify backups.
   • Update Oracle to Minimum Version: Ensure the Oracle database meets the minimum version requirements for DMO.
   • SAP System Update/EHP (if necessary): Ensure the SAP application (ECC, BW) meets the minimum release/EHP level required for the target HANA version or S/4HANA.
   • Implement SAP Notes: Apply all relevant SAP Notes for DMO, specific to your source database and target HANA version.
   • SPDD/SPAU Adjustments: Resolve any repository modifications if there's an application upgrade involved.
   • Master Data Cleansing: Beyond DVM, ensure master data consistency, remove duplicates, and fix errors. This improves data quality in the new system.
2. HANA Database Installation:
   • Install the SAP HANA database software on the prepared server.
   • Apply latest HANA SPS and Revision.
   • Configure HANA parameters as per SAP best practices.
3. DMO of SUM Setup:
   • Download the latest Software Update Manager (SUM) with DMO.
   • Place SUM in a dedicated directory on the Primary Application Server (PAS).
   • Start SUM and configure the migration scenario (e.g., database migration to HANA).

Phase 3: Execution - The Core Migration (using SUM DMO)

SUM DMO orchestrates the entire process in several phases, some of which are automated, combining a system update/upgrade with the database migration.⁵

1. Preparation Phase:
   • Source System Analysis: SUM analyzes the source SAP system and Oracle database.
   • Target System Configuration: Define target release (e.g., S/4HANA 2023), target HANA database.
   • Stack XML Generation: Use Maintenance Planner to generate a stack XML file that guides SUM.⁶
2. Extraction Phase (PREP_INPUT/EXTRACT):
   • SUM collects system parameters, profiles, and verifies prerequisites.⁷
   • Database-specific preparations are done on the Oracle side.
3. Configuration Phase (Configuration):
   • SUM presents various configuration options, like parallel processes (R3load, R3trans) for export/import, Unicode conversion options, etc.
   • Parallelism: Crucial for migration speed. Determine the optimal number of R3load processes based on CPU cores, memory, and I/O capacity of both source and target systems.
   • Schema Mapping: SUM handles the mapping of Oracle schemas to HANA schemas.⁸
4. System Downtime Begins (Execution Phase - Actual Migration Downtime):
   • Application Downtime: The SAP application servers are stopped. This is the main downtime window.
   • Data Export (from Oracle) & Import (to HANA) in Parallel:
     • SUM starts multiple R3load processes. One R3load process reads data from the Oracle database (export).
     • Simultaneously, this data is transferred via memory pipes to another R3load process that writes it directly into the HANA database (import). This eliminates the need for large export/import files on disk, significantly accelerating the migration.
     • Table Splitting: For very large tables, SUM automatically splits them into smaller packages to enable parallel processing and manage memory.
     • Data Type Conversion: Data types are converted on-the-fly from Oracle's types to HANA's types.
     • Columnar Store Conversion: Data is automatically converted to HANA's columnar store format during this phase.
   • DDIC Activation: Dictionary objects are activated for the new HANA database structure.⁹
   • Post-processing Steps: Indexes are created, statistics updated, and other database-specific tasks completed on HANA.
5. Post-Downtime / Downtime End:
   • Application Startup: SAP application servers are started against the new HANA database.
   • Post-Migration Activities:
     • Database Statistics Update: Essential for HANA's optimizer.
     • Consistency Checks: Run SAP-provided consistency checks (e.g., using DBACOCKPIT, SE38 reports) to verify data integrity.¹⁰
     • Performance Tuning: Initial performance monitoring and tuning of HANA.
     • Job Scheduling: Reconfigure background jobs if any database-specific commands were used.
     • Security: Configure HANA database users, roles, and privileges.

Phase 4: Post-Migration Activities & Go-Live

1. Functional Testing (Critical):
   • Unit Testing: Verify individual transactions and functionalities.
   • Integration Testing: Test end-to-end business processes involving multiple modules/systems.
   • User Acceptance Testing (UAT): Business users validate the system.
   • Performance Testing: Compare performance of key transactions and reports against baseline.
   • Interface Testing: Test all interfaces to and from the SAP system.
   • Reporting Verification: Ensure all reports (standard and custom) produce correct results.
2. Authorization Testing: Verify all user roles and authorizations.
3. Data Reconciliation:
   • Compare key business figures and record counts between the old Oracle system (if still available) and the new HANA system.
   • Use reports like RFUMSV00 for FI reconciliation, RAGITT01 for asset accounting.
4. Cutover Planning: Detailed plan for the final production migration.
5. Go-Live & Hypercare:
   • Execute the final cutover.
   • Provide intensive support to users immediately after go-live to address any issues promptly.
   • Continuous monitoring of system performance, resource utilization, and error logs.
6. Decommissioning (Optional): Once confidence is high, decommission the old Oracle database infrastructure.

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Key Points to Take Utmost Care Of:

1. Thorough Planning and Assessment (Phase 1):

   • Accurate Sizing: Incorrect HANA sizing is a common pitfall leading to performance issues or costly hardware re-procurement. Leverage SAP's sizing tools and engage experts.
   • Downtime Planning: Realistic downtime estimation is crucial. Business continuity must be considered. Data volume management is key to minimizing downtime.
   • Scope Definition: Clearly define what is being migrated, what is being left behind, and what new functionalities will be enabled.
   • Team Expertise: Ensure your team (internal or external) has deep expertise in Oracle, SAP Basis, SAP HANA, and the specific SAP application (ECC/BW/S/4HANA).
   • Stakeholder Communication: Keep business stakeholders informed about timelines, potential impacts, and progress.

2. Data Quality and Volume Management (Phase 1 & 2):

   • Data Cleansing: "Garbage in, garbage out" applies here. Cleanse master data and transactional data before migration to ensure a clean HANA system. Duplicate removal, error correction, and standardization are vital.
   • Archiving and Deletion: Reduce your database size significantly. This directly impacts migration downtime, HANA memory footprint, and future performance. It's often the most overlooked but impactful step.

3. Custom Code Adaptation (Phase 1 & 3):

   • Pre-analysis: Identify and assess all custom code (ABAP, native SQL, reports, interfaces, enhancements, modifications).
   • Remediation: Adapt custom code for HANA's column store and in-memory capabilities. This often means optimizing SQL statements, avoiding "SELECT *" without WHERE clauses, handling database-specific hints, etc. Tools like ATC are indispensable. This can be a significant effort and source of post-migration issues if not handled meticulously.

4. Backup and Recovery Strategy (All Phases):

   • Robust Backups: Ensure reliable and tested backups of the source Oracle database before migration.
   • HANA Backup Plan: Establish a comprehensive backup and recovery strategy for the new HANA database immediately after its installation and throughout the migration and hypercare phases. Test recovery procedures.

5. Testing Strategy (Phase 4):

   • Comprehensive Testing: Do not compromise on testing. This includes functional, integration, user acceptance, and especially performance testing.
   • Data Validation: Implement rigorous data reconciliation methods. Compare key figures and record counts. Validate critical business reports.
   • Regression Testing: Ensure existing functionalities work as expected after migration.
   • Performance Benchmarking: Establish baselines before migration and compare post-migration to confirm performance improvements or identify bottlenecks.

6. Optimal Parallelism (Phase 3):

   • DMO Performance: Correctly configure the number of R3load and R3trans processes in SUM DMO. This directly influences the migration downtime. Too few, and it's slow; too many, and it can overwhelm the source or target, leading to errors or instability. Monitor CPU, I/O, and memory during test migrations to fine-tune.

7. Network Stability and Performance (All Phases):

   • High-Bandwidth Network: Ensure a stable, high-bandwidth, low-latency network connection between the SAP application servers and the new HANA database server. This is critical for both the migration itself and ongoing application performance.

8. Post-Migration Optimization:

   • Statistics and Indexing: Immediately after migration, ensure database statistics are updated and optimized. Recreate secondary indexes where beneficial (though HANA relies less on them due to its architecture).
   • Workload Analysis: Monitor HANA's performance using HANA Studio/Cockpit and identify long-running queries or bottlenecks.¹¹

9. Fallback Plan:

   • Always have a well-defined fallback plan in case of unforeseen critical issues during the cutover. This usually involves reverting to the old Oracle system from a recent backup.

By meticulously addressing these key areas, organizations can significantly de-risk the complex journey of migrating their SAP database from Oracle to SAP HANA, unlocking the power of in-memory computing for their business.