DynamoDB global index overloading vs sparse indexes

2
votes

We are designing an application which will use DynamoDB as storage system.

We identified the different access patterns and after reviewing Global Secondary Indexes documentation, we got stuck on making a decision about which approach to use: Index overloading or having 2 sparse index.

To give more context, our application stores orders, we can have internal or external orders. Based on that, they will be linked to a Customer or a Warehouse:

Data model

As we would like to search by customer and/or warehouse we thought about 2 solutions.

First solution would be, keeping the above data structure, creating 2 indexes on:

  • GSI1 - Customer (PK)
  • GSI2 - Warehouse (PK)

Second solution is to overload another column like:

Index overloading

So only 1 index required: Destination (PK), and queried applies with a prefix.

The question is: "Is there any benefit between index overloading over having 2 different sparse Global Secondary Indexes?" (Cost saving on capacity provisioning, data transport, query times, data complexity...)

1
amazon-dynamodbamazon-dynamodb-index

1 Answers

1
votes

As I didn't get any answer yet, I'll add my opinion.

There is no big difference between the 2 approaches in both cases all items will end up being indexed and similar attributes stored.

Some benefits I could find are:

Benefits using 2 GSI

  1. Data schema is easier to understand (no overloading)
  2. More flexibility for evolving the schema: if requirements change, an order can be assigned to both a customer and a warehouse.
  3. Capacity to adjust better projections (may not be always applicable, but you may only need 2 fields for Customer access pattern and 3 for Warehouse)
  4. Smaller indexes have greater performance

Benefits using 1 GSI

  1. No need to worry about capacity units, they can be similar to main table. When using 2 indexes, you need to know an estimation of how many records will fall under each of them, otherwise you need to over-provision them.

    Example: If you set 50% RCU and WCU from main table to each of the indexes, but you have 70% orders which are for customers, some requests will be throttled.

In summary, even using 2 indexes allows to get a more precise configuration, it may end up having a higher cost and the need to review index configuration to adjust it to access patterns usage from time to time.