9.3: Don’t reuse attributes across multiple indexes

As discussed, you will have indexing attributes that are solely for properly indexing your data in DynamoDB. Let’s print out a dummy User object to see its attributes.

        {
            "PK": { "S": "USER#antonychiramel" },
            "SK": { "S": "USER#antonychiramel" },
            "GSI1PK": { "S": "ORG#facebook" },
            "GSI1SK": { "S": "USER#antonychiramel" },
            "Username": { "S": "antonychiramel" },
            "FirstName": { "S": "Antony" },
            "LastName": { "S": "Chiramel" },
            "OrganizationName": { "S": "Facebook" },
            ...
        }

You may notice that SK and GSI1SK are the same value. And because they’re the same value, you may be tempted to skip adding GSI1SK altogether and make your GSI1 index use a key schema of GSI1PK and SK.

Don’t do this.

While you are saving some money in storage by not duplicating attributes, it will make your data modeling more difficult. Save yourself the pain. For each global secondary index you use, give it a generic name of GSI<Number>. Then, use GSI<Number>PK and GSI<Number>SK for your attribute types.