Amazon DynamoDB

AWS Tips I Wish I'd Known Before I Started

• DynamoDb is a noSQL schema-less storage. Each entity can have different attributes. Total item/entity size 64 KB (UTF-8), name and value count towards size
• Maximum tables 256/region/account, can request limit increase
• No practical limit in table size, bytes or items
• Attributes are name=value pairs and can be single value or multi-value set
• Attribute types: String, binary, number (38 digits of precision after the decimal point, and can be between 10^-128 to 10^+126), or sets, no empty values or sets
• Idempotent conditional updates: only applied if conditions are met, safe to retry in the event of failure to acknowledge
• Atomic counters: increment/decrement, not idempotent, use conditional for idempotent
• Consistent reads consume more resources, time, and cost more money (avoid them when possible)
• Must create indexes when tables are created, can't update, add or delete later
• Hash key distributes data among resources
• Range key partitions data
• Query is more efficient than scan, scan reads every record in the table
• Scanning always scans the entire table, slows as table grows, can consume entire provisioned throughput in a single operation
• Scan imposes 1 MB limit before filtering
• Must pre-configure read/write capacity for tables when created
• Automatic result pagination in 1 MB increments
• Result limits can be imposed
• Scans by default are sequential, can specify degree of parallelism
• Best Practices

Indexes

• Must create indexes during table create, can't update, add or delete later

Local Secondary Indexes

• Hash must be same as tables PK hash plus some other table attribute for a range key
• Each hash key is limited to 10 GB for all indexed items
• Can only query over single partition based on range key
• Queries can be either eventual or strong consistency
• Can request data not projected in the index

Global Secondary Indexes

• Hash and range can be any table attribute
• No limit on size
• Can query over entire table
• Queries can only be eventual consistency
• Can only request data projected in the index