DynamoDb Eventual Consistency: the index or the record?

Question

In DynamoDb, reads using Global Secondary Indexes are eventually consistent by default: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GSI.html#GSI.Querying

However, does that mean queries to a GSI may return one of the following:

1. The old set of records with the old values
2. The old set of records with the new values
3. The new set of records, but the attributes of the record will be old

Example for clarification:

• Table Foo has 3 fields: a, b, c
• Foo has a primary key a and a GSI on b

• Foo starts with the following records: {a: 1, b: apple, c: blue} {a: 2, b: orange, c: green}

• A write to foo updates the record where a = 2 to be: {a:2, b: apple, c: red}

• Another write updates the record where a = 1 to be: {a: 1, b: apple, c: orange}

• After the write, suppose there is some delay and before the GSI is consistent, a read is made to the table using the GSI

• The query uses the GSI to get all records where b = apple

• Will this query return:

Result X - Wrong Set but Right Attribute Values: {a: 1, b: apple, c: orange}

Result Y - Right Set but Wrong Attribute Values: {a: 1, b: apple, c: blue} {a: 2, b: orange, c: green}

Result Z - Wrong Set and Wrong Attribute Values: {a: 1, b: apple, c: blue}

or something else?

Answer 1

Queries on the GSI will sometimes return the old set of records

Yes

Queries will return the new set of records, but the attributes of the record will be old?

This will never happen.