DynamoDB

What is it?

• AWS's fully-managed, serverless NoSQL database
• Stored on SSDs across multiple AZs
• Serverless key-value/document NoSQL database
• Consistent single-digit ms performance (µs with DAX) at any scale (>20M reqs/sec)
• Encrypted, steams, instant backup, point-in-time recovery, HA, auto-scaling tables and storage, ACID transaction, pay-per-use, IAM
• Eventually consistent by default with support for strongly consistent reads
• Available DynamoDB Encryption Client in Java, can be used with KMS, CloudHSM, or your own keys

Why use it?

• Cursor-based paging eliminates timeouts and duplicate results
• No performance impact for new columns
• No need to cluster and/or shard in future
• Plays nicely with AWS Lambda

Limitations

• RDBMS: flexible queries, but expensive, less scale
• NoSQL: efficient queries in limited number of ways, other queries are expensive, slow
• Essential to understand access patterns up-front
• Amazon migrated 90% of their systems to Dynamo, it fits more data models than you realize
• Cursor-based paging would require either adapter to support limit/offset or new API version
• No COUNT, must be calculated separately

Data Modeling Approach

• Create Entity-Relationship model as usual

• List all real-time client access patterns

• Ignore reporting, search, etc., use streams for this

• If ad-hoc queries are required, stick to SQL

• Design one table to store your entities with high-cardinality keys, possibly with overloaded indexes and composite sort keys

• One-To-Many via Composite SK, table can be queried by pk and starts_with, between, >, < etc.

• Index Overloading

  

  • One table, one GSI - Table can be queried by ID for accounts and todo entities - GSI can be queried for accounts by status and for todos by account

• Many-To-Many

  

  • One table, one GSI - Table can be queried by ID for accounts and todo entities and for todos per account - GSI can be queried for accounts by todo

Resources

• How to switch from RDBMS to DynamoDB in 20 easy steps, videos linked in article are great
• Best Practices
• NoSQL Workbench
• DynamoDB Toolbox
• Alex DeBrie's guide and book