How I Migrate My Clients’ SQL Databases To DynamoDB

Migrating from a SQL database to DynamoDB is not a one-size-fits-all decision.

It requires a deep understanding of access patterns, data modeling techniques, and costs. I only recommend this migration when there are clear performance or cost benefits.

Here’s the structured approach I take when helping clients transition from SQL to DynamoDB.

1. I Define Access Patterns First

In SQL, data is normalized into multiple tables with relationships managed with foreign keys.

However, in DynamoDB, the design is actually based on how the application queries and writes data.

Before starting any migration, I like to list out every access pattern on the application. In other words, how data will be read and written.

This step ensures that the database structure supports efficient queries without increases in cost or latency.

2. I Choose the Right Primary Keys

DynamoDB does not support traditional SQL joins.

Instead, it relies on partition and sort keys. The selection of these keys directly impacts performance and scalability.

A poor key selection can lead to hot partitions, causing slowdowns and increased costs.

Because of this, I spend the most amount of time in the migration/design process defining my primary keys to ensure an efficient and scalable data model.

3. I Denormalize Data Where Needed

Unlike SQL, where data is spread across multiple tables and joined together at query time, DynamoDB takes advantage of denormalization instead.

This means I’ll embed related data into a single item to reduce the number of read operations, which means duplicating data when necessary.

By doing so, queries become faster and more efficient, avoiding expensive join-like operations in NoSQL; the primary latency reasons for SQL databases.

4. I Use Global Secondary Indexes (GSIs) Instead of SQL Indexes

SQL databases allow multiple indexes, but DynamoDB takes a different approach with GSIs.

If an application requires querying data based on different attributes, I strategically implement GSIs.

To optimize costs and performance, I apply key overloading, which allows me to use a single index for multiple query patterns rather than creating multiple GSIs.

5. I Handle Transactions Differently

DynamoDB supports transactions, but they come at twice the cost in terms of read and write capacity units.

Instead of relying on transactions as frequently as in SQL, I use a single-table design with transactional writes only when necessary.

This keeps operations efficient while maintaining data consistency.

6. I Test and Optimize Queries

Every access pattern must be tested to ensure that the new database performs efficiently.

I evaluate query performance, monitor read and write capacity usage, and optimize indexing strategies before fully transitioning to DynamoDB.

Sometimes I may have to change a primary key design or a GSI to support a better access pattern.

Other times, my clients may present me a revised or improved access pattern and I will then have to adjust my data model accordingly.

Once everything is accounted for, it is time for the actual migration process.

My Preferred Migration Strategy: Dual-Write Approach

To ensure a smooth transition with minimal downtime, I typically implement a dual-write strategy.

Here’s the step-by-step flow:

• Both the SQL database and DynamoDB receive new data writes.
• Reads continue to be served from the SQL database.
• Once the DynamoDB setup is validated and optimized, I’ll start cutting over read operations to it.
• After confirming stable performance (may take a few days to a few weeks), the SQL database is disconnected.
• DynamoDB becomes the primary database

This gradual cutover method makes sure the migration is as smooth as possible while allowing time to validate data consistency and query performance.

Conclusion

Migrating from SQL to DynamoDB is not just about moving data; it requires, as I often say “a shift in mindset”.

SQL focuses on normalization and relationships, whereas DynamoDB is built for scalability and optimized query performance.

By carefully defining access patterns, choosing the right keys, denormalizing where necessary, using GSIs, and implementing an effective migration strategy, you can achieve a smooth and cost-efficient transition from any database to DynamoDB.