Build Leaderboard with DynamoDB GSI

Question

I'm going to create Leaderboard using this example as a reference.
https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GSI.html

There are two access patterns.
1. Get Top 100
```
{
    "TableName": "GameScores",
    "IndexName": "GameTitleIndex",
    "KeyConditionExpression": "GameTitle = :v_title",
    "ExpressionAttributeValues": {
        ":v_title": {"S": "Meteor Blasters"}
    },
    "ProjectionExpression": "UserId, TopScore",
    "ScanIndexForward": false,
	"Limit": 100
}
```

2. Get My Rank

```
{
    "TableName": "GameScores",
    "IndexName": "GameTitleIndex",
    "KeyConditionExpression": "GameTitle = :v_title and TopScore > :score",
    "ExpressionAttributeValues": {
        ":v_title": {"S": "Meteor Blasters"},
	":score": {"N": myScore},
    },
    "ScanIndexForward": false,
    "Select": COUNT	
}
```

Is this a good idea? I'm concerned that Getting My Rank will get slower as slower as getting more and more items like millions of items.

Leeroy Hannigan · Accepted Answer

DynamoDB would not be my go-to for a leaderboard, as other better alternatives exist. But i'm assuming here that you want to use a single database (DynamoDB) for your entire application....

While your first access pattern is highly efficient, your second one may not be as scalable. Imagine 1M players played the game `Meteor Blasters` and your rank is last place, you have to read 999,999 items to understand where you are in the list. That's going to be slow and expensive.

I would consider updating the users game rank on a daily basis for example, especially if they are not explicitly asking for it and its just used to populate a dashboard.

Build Leaderboard with DynamoDB GSI

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