AWS DynamoDB

Quick Reference

All patterns are in references/dynamodb-patterns.md.

Topic	Key Insight
Data modeling	Design access patterns FIRST, schema second
Single-table design	Items queried together live together
GSIs	Multi-attribute composite keys avoid synthetic key hacks
Cost optimization	Filter expressions do NOT reduce read costs
Sort order control	`#` prefix positions parent at sort boundary; numeric difference enables reverse integer ordering
Sparse indexes	Entity-type filter (always-on attr) vs conditional filter (add/remove attr on state change)
Reference counts	TransactWriteItems: child PutItem (attribute_not_exists) + parent UpdateItem increment
Hot partitions	Timestamp-shard GSI PK by day; read-shard caches across N copies
Many-to-many	Adjacency list: link item in base table + GSI projects into second parent's collection
Uniqueness enforcement	Uniqueness tracking item (no data) + TransactWriteItems with attribute_not_exists on each