DynamoDB

Keys

SK on table is optional
primary key is PK + SK
query
- PK is required
- SK is optional
put & delete
- item based actions
- need both PK & SK (i.e. the full primary key)

Indexes

local secondary index
- same PK as table, but different SK
  - i.e. "local" on each partition
- must be created with table

Tips

ulid lexically cronologically sortable unique id
use conditionExpression: "attribute_not_exists(PK)" with PutItem to ensure you don't overwrite existing entry.
when getting DynamoDB client add httpOptions: { connectTimeout: 1000, timeout: 1000} to add 1s timeout
use transactions to make multiple operations in one request - they all succeed or fail together (with rollback)
UpdateExpression: "SET #likesCount = #likescCount += :inc" increment with atomicity (otherwise you'll need to do a separate get first)
batchGetItem() single request to query 100 items (total 16MB data). Returns list of unprocessed keys if limit reached.