NoSQL database systems like Amazon DynamoDB use alternative models for data management, such as key-value pairs or document storage. When you switch from a relational database management system to a NoSQL database system like DynamoDB, it’s important to understand the key differences and specific design approaches.
Differences Between Relational Data Design and NoSQL
Relational database systems (RDBMS) and NoSQL databases have different strengths and weaknesses:
- In RDBMS, data can be queried flexibly, but queries are relatively expensive and don’t scale well in high-traffic situations (see First Steps for Modeling Relational Data in DynamoDB).
- In a NoSQL database such as DynamoDB, data can be queried efficiently in a limited number of ways, outside of which queries can be expensive and slow.
These differences make database design different between the two systems:
- In RDBMS, you design for flexibility without worrying about implementation details or performance. Query optimization generally doesn’t affect schema design, but normalization is important.
- In DynamoDB, you design your schema specifically to make the most common and important queries as fast and as inexpensive as possible. Your data structures are tailored to the specific requirements of your business use cases.
Two Key Concepts for NoSQL Design
NoSQL design requires a different mindset than RDBMS design. For an RDBMS, you can go ahead and create a normalized data model without thinking about access patterns. You can then extend it later when new questions and query requirements arise. You can organize each type of data into its own table.
How NoSQL design is different
- By contrast, you shouldn’t start designing your schema for DynamoDB until you know the questions it will need to answer. Understanding the business problems and the application use cases up front is essential.
- You should maintain as few tables as possible in a DynamoDB application.
Approaching NoSQL Design
The first step in designing your DynamoDB application is to identify the specific query patterns that the system must satisfy.
In particular, it is important to understand three fundamental properties of your application’s access patterns before you begin:
- Data size: Knowing how much data will be stored and requested at one time will help determine the most effective way to partition the data.
- Data shape: Instead of reshaping data when a query is processed (as an RDBMS system does), a NoSQL database organizes data so that its shape in the database corresponds with what will be queried. This is a key factor in increasing speed and scalability.
- Data velocity: DynamoDB scales by increasing the number of physical partitions that are available to process queries, and by efficiently distributing data across those partitions. Knowing in advance what the peak query loads might help determine how to partition data to best use I/O capacity.
After you identify specific query requirements, you can organize data according to general principles that govern performance:
- Keep related data together. Research on routing-table optimization 20 years ago found that “locality of reference” was the single most important factor in speeding up response time: keeping related data together in one place. This is equally true in NoSQL systems today, where keeping related data in close proximity has a major impact on cost and performance. Instead of distributing related data items across multiple tables, you should keep related items in your NoSQL system as close together as possible.As a general rule, you should maintain as few tables as possible in a DynamoDB application.Exceptions are cases where high-volume time series data are involved, or datasets that have very different access patterns. A single table with inverted indexes can usually enable simple queries to create and retrieve the complex hierarchical data structures required by your application.
- Use sort order. Related items can be grouped together and queried efficiently if their key design causes them to sort together. This is an important NoSQL design strategy.
- Distribute queries. It is also important that a high volume of queries not be focused on one part of the database, where they can exceed I/O capacity. Instead, you should design data keys to distribute traffic evenly across partitions as much as possible, avoiding “hot spots.”
- Use global secondary indexes. By creating specific global secondary indexes, you can enable different queries than your main table can support, and that are still fast and relatively inexpensive.
These general principles translate into some common design patterns that you can use to model data efficiently in DynamoDB.
WHAT IS DYNAMO DB?
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Amazon DynamoDB is a fully managed NoSQL database service that provides fast and predictable performance with seamless scalability. DynamoDB lets you offload the administrative burdens of operating and scaling a distributed database so that you don’t have to worry about hardware provisioning, setup and configuration, replication, software patching, or cluster scaling. DynamoDB also offers encryption at rest, which eliminates the operational burden and complexity involved in protecting sensitive data. For more information, see DynamoDB Encryption at Rest.
With DynamoDB, you can create database tables that can store and retrieve any amount of data and serve any level of request traffic. You can scale up or scale down your tables’ throughput capacity without downtime or performance degradation. You can use the AWS Management Console to monitor resource utilization and performance metrics.
DynamoDB provides on-demand backup capability. It allows you to create full backups of your tables for long-term retention and archival for regulatory compliance needs. For more information, see On-Demand Backup and Restore for DynamoDB.
You can create on-demand backups and enable point-in-time recovery for your Amazon DynamoDB tables. Point-in-time recovery helps protect your tables from accidental write or delete operations. With point-in-time recovery, you can restore that table to any point in time during the last 35 days. For more information, see Point-in-Time Recovery: How It Works.
DynamoDB allows you to delete expired items from tables automatically to help you reduce storage usage and the cost of storing data that is no longer relevant. For more information, see Expiring Items By Using DynamoDB Time to Live (TTL).
High Availability and Durability
DynamoDB automatically spreads the data and traffic for your tables over a sufficient number of servers to handle your throughput and storage requirements, while maintaining consistent and fast performance. All of your data is stored on solid-state disks (SSDs) and is automatically replicated across multiple Availability Zones in an AWS Region, providing built-in high availability and data durability. You can use global tables to keep DynamoDB tables in sync across AWS Regions. For more information, see Global Tables: Multi-Region Replication with DynamoDB.
Getting Started with DynamoDB
We recommend that you begin by reading the following sections:
- Amazon DynamoDB: How It Works—To learn essential DynamoDB concepts.
- Setting Up DynamoDB—To learn how to set up DynamoDB (the downloadable version or the web service).
- Accessing DynamoDB—To learn how to access DynamoDB using the console, AWS CLI, or API.
To get started quickly with DynamoDB, see Getting Started with DynamoDB and AWS SDKs.
To learn more about application development, see the following:
To quickly find recommendations for maximizing performance and minimizing throughput costs, see Best Practices for Designing and Architecting with DynamoDB. To learn how to tag DynamoDB resources, see Adding Tags and Labels to Resources.
For best practices, how-to guides, and tools, see Amazon DynamoDB resources.
You can use AWS Database Migration Service (AWS DMS) to migrate data from a relational database or MongoDB to a DynamoDB table. For more information, see the AWS Database Migration Service User Guide.
To learn how to use MongoDB as a migration source, see Using MongoDB as a Source for AWS Database Migration Service. To learn how to use DynamoDB as a migration target, see Using an Amazon DynamoDB Database as a Target for AWS Database Migration Service.