Reads and cost · Lesson 3 of 20

One query, a whole collection

Items that share a partition key are read together in one Query.

Next · Reads and costThe sort key is a query language→

Why

All the items sharing a partition key form an item collection, stored together and sorted by sort key. Query reads a slice of one collection.

Here one Query returns the room and every message in it, in order, in a single round trip. The messages were written next to the room on purpose, so reading them back is one cheap operation rather than a join.

Co-locate what you read together. Then a Query reads it all at once, cheaply.

Chatdynoxide · wasm · DynamoDB API 2012-08-10 · contract 1

Try an example

Every item under ROOM#general, the room meta and all its messages, in a single request.

Indexoptionalbase table, or a secondary indexKeyConditionExpressionFilterExpressionoptionalExpressionAttributeValues

pk(pk)

sk(sk)

topic

from

text

Run an operation to see the raw engine response.

table Chatkeys pk / skitems 22