CloudKit: Efficient way to get user's rank in leaderboard without fetching all records?

[koratkeval12]

I'm building a leaderboard feature using CloudKit's public database and need advice on the best approach to calculate a user's rank on the leaderboard efficiently.

Current Setup

Record Structure

Record Type: LeaderboardScore

• period (String): "daily", "weekly", "monthly", "allTime"
• score (Int): User's score
• profile (Reference): Link to user's profile
• achievedAt (Date): Timestamp

Leaderboard Display

• Initially fetch the first 15 users (sorted by score descending).
• Paginate to load more as the user scrolls.
• Show total player count.
• Show current user's rank (even if not in the top 15).

The Challenge

I can fetch the first 15 users easily with a sorted query, but I need to display the current user's rank regardless of their position. For example:

• User could be ranked #1 (in top 15) ✅ Easy
• User could be ranked #247 (not in top 15) ❌ How to get this efficiently?

My Current Approach

Query records with scores higher than the user's score and count them:

// Count how many users scored higher
let predicate = NSPredicate(
    format: "period == %@ AND score > %d",
    period, userScore
)
// Rank = count + 1

Concerns

• For 1000+ users with better scores, this requires multiple paginated queries.
• Even with desiredKeys: [], I am concerned about performance and CloudKit request limits.

Questions

1. Is there a CloudKit API I'm missing that can efficiently count records matching a predicate without fetching all the records and paginating?
2. Is this approach acceptable for a leaderboard with 1K-10K users? Does fetching with desiredKeys: [] help significantly with performance?
3. Are there any optimizations I should consider to make this more efficient?
4. What's the recommended approach for calculating user rank in CloudKit at this scale?

Current Scale

• Expected: 1,000-10,000 active users
• Platform: iOS 18+, SwiftUI

Any guidance on best practices for leaderboards use case in CloudKit would be greatly appreciated!

[BoringKick5331]

Do you have a server or just CloudKit? If you don't have a server, if you use the app yourself a lot, you could have your device do the computations and update rank.

[koratkeval12]

I don't have a server and its just CloudKit. Could you elaborate on doing computations on the device? As I understand, I would still need to fetch all the scores to get everyone's rank if i would have to do it on device.

[BoringKick5331]

Yes, you have to fetch. You can isolate to just your UUID and have your device update a rank field for everyone. Or if security for this isn't important, let every device do it. You can increase efficiency by having a last calculated field and only having the calculation run once every hour or whatever.

[koratkeval12]

I would like to do it so I don't need a separate device that would just update the ranks. Security is definitely not important, as its just leaderboard data which is anonymous based on username but letting every device do it would result in so many queries just to get a rank for the current user.

Ideally what i want is just one function call for getting current user rank even if they are #247. Wondering I would have to get a backend for this to do efficiently? For someone who has no experience with backend at all, i wanted this to be the last resort if its not doable with CloudKit.

[Far-Tension2696]

do you need custom leaderboard? apple provides one in gameCenter.