SQL Server to Azure Synapse Analytics: 10TB Migration Case Study

A large US retail chain with 500+ stores was running a 10TB on-premises SQL Server data warehouse that had become a critical bottleneck. Query response times had degraded to 30 minutes for executive reports. Numlytics delivered a complete zero-downtime migration from SQL Server to Azure Synapse Analytics, moving 2,000+ tables and 10TB of data in 16 weeks with zero reporting disruption, and achieving 8x faster query performance on the same workload.

The Challenge: On-Premises Data Warehouse Becoming a Business Bottleneck

The retailer had invested significantly in its on-premises SQL Server data warehouse over a decade. With 500+ stores and 2,000+ tables, it had become the central analytical backbone. However, hardware was aging, and query performance had degraded unacceptably.

• Query performance degradation: Executive reports that once ran in five minutes now took 30 minutes, making ad-hoc analysis impossible and frustrating users.
• Capacity constraints: Adding new data or increasing refresh frequency was constrained by hardware limitations and required expensive infrastructure additions.
• Aging infrastructure: Hardware was 8 years old with increasing maintenance costs and reliability concerns.
• On-premises operational burden: The data team spent 40% of time on hardware maintenance rather than analytics work.

The Numlytics Approach: Zero-Downtime Synapse Migration

Numlytics designed a five-phase migration strategy that ran both SQL Server and Azure Synapse Analytics in parallel until cutover, ensuring that business users never experienced disruption and data quality was validated at every stage.

1. 01
   Discovery and Schema Assessment

   Complete inventory of all 2,000+ tables, 50,000+ stored procedures, schemas, and data lineage. Datatype compatibility analysed between SQL Server and Synapse, with migration mapping for edge cases.

2. 02
   Azure Infrastructure and Synapse Architecture

   Azure Synapse Dedicated SQL Pool provisioned with distribution strategy optimised for the retailer's query patterns. Staging databases created for testing and validation before production cutover.

3. 03
   Parallel Load and Testing

   While the original SQL Server continued to serve reports, Azure Data Factory pipelines loaded all 10TB of data into Synapse using DMS (Data Migration Service). Each table was validated against source for row counts and data integrity.

4. 04
   Query Rewrite and Performance Tuning

   Stored procedures and reporting queries tested against Synapse and rewritten where needed to take advantage of Synapse's massively parallel processing architecture. Executive reports validated to run in under 2 minutes.

5. 05
   Cutover and Decommission

   SQL Server cut over to Synapse during a planned maintenance window. Business users saw no downtime. On-premises hardware decommissioned within 30 days, reducing operational costs immediately.

The Results

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