Dynamo DB leader board within an Alexa Skill - amazon-dynamodb

Question

I am attempting to create a leader board using dynamo db for an quiz style Alexa skill. I have set up the table and users are added to the table with their appropriate data e.g.:
Item: {
"PlatformId": 2,
"UserId": 12345,
"Score": 100,
"NickName": "scott",
"Sport": "football",
}
In my table the Primary key is their UserId, the sort key is the PlatformId (this is the same for all users). I have a secondary global index which sets the platformId as the primary key, and the score as the sort key.
In this leader board i want users to be ranked, the highest scorer being number 1, my first attempt at this was to scan the table using the secondary index, this nicely returned all the users sorted by score, however with the potential to have thousands of users on this leader board, i discovered that the time to scan a table with 10000+ users exceeds the 8 second response time that Alexa skills have. This causes the skill to error and close.
Before the response time exceeded, i was using the LastEvaluatedKey to perform an extra scan if the first one didn't cover the entire table, but on this second scan is when the response time limit was exceeded. Annoyingly it's just taking too long to scan the table.
dbHelper.prototype.scanGetUsers = (ad, newParams = null) => {
return new Promise((resolve, reject) => {
let params = {};
if (newParams != null) {
params = newParams
} else {
params = {
TableName: tableName,
IndexName: 'PlatformId-Score-index',
FilterExpression: "Score >= :s AND PlatformId = :p",
ProjectionExpression: `NickName, Sport, Score`,
// Limit: 10,
ExpressionAttributeValues: {
":p": User.PlatformId,
":s": User.Score,
},
}
}
docClient.scan(params, function (err, data) {
if (err || !data) {
console.error("Unable to read item. Error JSON:", JSON.stringify(err, null, 2));
return reject(JSON.stringify(err, null, 2))
} else {
console.log("scan users data succeeded:", JSON.stringify(data, null, 2));
if(data.LastEvaluatedKey) {
console.log("found a LastEvalutedKey, Continuing scan");
params.ExclusiveStartKey = data.LastEvaluatedKey;
data = data.concat(this.scanGetUsers(ad, params));
}
resolve(data);
}
});
});
}
Is there a way to work around these issues that i haven't explored yet? Or a way to create a leader board with dynamo db that can be structured in an easier way?

Answer 1

You can try Sort Key:
When you combine a partition key and sort key, they create a composite key, and that composite key is the primary key for individual items in a table. With a composite key, you gain the ability to use queries with a KeyConditionExpression against the sort key. In a query, you can use KeyConditionExpression to write conditional statements by using comparison operators that evaluate against a key and limit the items returned. In other words, you can use special operators to include, exclude, and match items by their sort key values.
The article contains all information how to setup and use it.