2.1.4.2. DynamoDB Partition Keys & Indexing (GSI, LSI)
2.1.4.2. DynamoDB Partition Keys & Indexing (GSI, LSI)
First Principle: Proper DynamoDB Partition Key design is crucial for even data distribution, enabling high throughput. Indexes (GSI, LSI) provide flexible query patterns beyond the primary key.
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The primary key in Amazon DynamoDB (consisting of a Partition Key and optional Sort Key) is fundamental to how data is distributed and accessed. For queries beyond the primary key, secondary indexes are essential.
- Partition Key (Hash Attribute):
- Purpose: Determines the physical partition (storage location) for each item.
- Importance: A good Partition Key distributes data evenly across partitions to prevent "hot spots" (partitions receiving disproportionately high traffic), which can lead to throttling and poor performance.
- Example: For a "User" table,
UserIdas the Partition Key is good if user IDs are diverse.
- Sort Key (Range Attribute):
- Purpose: Defines the order of items within a partition. Allows for efficient range queries.
- Example: In an "Order" table,
CustomerIdas Partition Key andOrderIdas Sort Key allows querying all orders for a customer sorted by order ID.
- Secondary Indexes: Provide alternative access patterns to your table data, allowing you to query on attributes other than the primary key.
- Global Secondary Index (GSI): A new table with a different Partition Key (and optional Sort Key) than the base table. Can span all partitions of the base table. Used for frequently accessed, non-primary key attributes. Data is eventually consistent.
- Local Secondary Index (LSI): Has the same Partition Key as the base table, but a different Sort Key. Queries are scoped to a single partition key value. Data is strongly consistent.
Scenario: You're designing a DynamoDB table to store e-commerce orders. You want to efficiently retrieve orders by OrderId (unique) and also query all orders for a given CustomerId (many orders per customer), and frequently look up orders by ProductSKU (many orders per SKU).
ā ļø Exam Trap: LSI must be created at table creation and shares the table's partition key. GSI can be created anytime and has its own partition key. LSI supports strongly consistent reads; GSI only supports eventually consistent reads.
