Migrating from a relational database (SQL) like MySQL, PostgreSQL, or Oracle to a NoSQL database like MongoDB, Cassandra, or DynamoDB requires careful schema transformation, data restructuring, and query modification.
1. Assess & Choose the Right NoSQL Database
* Identify the use case :
- Document-based (MongoDB, CouchDB) → Best for semi-structured data (JSON).
- Key-Value Store (DynamoDB, Redis) → Best for fast lookups.
- Column-based (Cassandra, HBase) → Best for analytics & distributed data.
- Graph-based (Neo4j, ArangoDB) → Best for relationship-heavy data.
* Analyze SQL database structure, including :
- Tables & relationships
- Primary & foreign keys
- Indexing & constraints
2. Design the NoSQL Schema :
* SQL Schema → NoSQL Schema Mapping :
- Tables → Collections (MongoDB) or Column Families (Cassandra)
- Rows → Documents (MongoDB) or Columns (Cassandra)
- Primary Key → Partition Key (Cassandra, DynamoDB)
- Joins → Embedded documents (MongoDB) or Denormalization
* Flatten relational data :
- Instead of normalizing with joins, embed related data (for faster queries).
- Example: A
Users table with multiple Addresses → Store addresses as an array inside a Users document in MongoDB.
3. Extract, Transform, Load (ETL) Process :
* Extract: Dump SQL data (CSV, JSON, or BSON format).
* Transform: Convert relational rows into NoSQL-compatible JSON documents or key-value pairs.
* Load: Use batch inserts or NoSQL migration tools:
- MongoDB:
mongoimport, PyMongo.
- Cassandra:
COPY, sstableloader.
- DynamoDB: AWS DMS (Database Migration Service).
4. Modify Queries & Application Logic :
* Convert SQL queries to NoSQL equivalents:
SELECT * FROM users WHERE id = 1;
* MongoDB: { _id: 1 }
* Cassandra: SELECT * FROM users WHERE id = 1;- Replace joins with document embedding or application-side joins.
- Optimize for NoSQL query patterns (denormalization, indexing).
5. Optimize & Test Performance :
* Indexing :
- Use compound indexes (MongoDB) or partitioning keys (Cassandra).
- Avoid full-table scans by optimizing query patterns.
* Validation :
- Compare record counts between SQL & NoSQL.
- Use checksums or hashes to validate data integrity.
- Perform load testing to check query performance.
6. Deploy & Monitor :
* Deploy in phases (start with read-heavy queries before full migration).
* Set up monitoring tools (CloudWatch for DynamoDB, Prometheus for Cassandra).
* Continuously optimize schema & queries based on performance.
