found the actual culprit that destroyed my performance - 10x'd it now, seems much more stable, too

Author: Robert Quander

service/Sources/App/Models/IdentifierGenerator.swift

@@ -2,19 +2,24 @@ import Foundation
 
 final class IdentifierGenerator {
     static func generate(from username: String) -> UUID {
-        var usernameBytes = [UInt8](username.utf8)
+        var usernameBytes = [UInt8](username.utf8.prefix(16))
         while usernameBytes.count < 16 {
             usernameBytes.append(95)
         }
-    
-        if usernameBytes.count > 16 {
-            usernameBytes = Array(usernameBytes.prefix(16))
-        }
-        let hex = usernameBytes.map { String(format: "%02x", $0) }.joined()
 
-        let formatted = "\(hex.prefix(8))-\(hex.dropFirst(8).prefix(4))-\(hex.dropFirst(12).prefix(4))-\(hex.dropFirst(16).prefix(4))-\(hex.dropFirst(20))"
+        let uuid = uuidFromBytes(usernameBytes)
+        return uuid
+    }
 
+    private static func uuidFromBytes(_ bytes: [UInt8]) -> UUID {
+        let hex = String(bytes.lazy.map { hexLookup[Int($0)] }.joined())
+        let formatted = hexToUUIDString(hex)
         return UUID(uuidString: formatted) ?? UUID()
     }
 
-}
+    private static let hexLookup: [String] = (0...255).map { String(format: "%02x", $0) }
+
+    private static func hexToUUIDString(_ hex: String) -> String {
+        return "\(hex.prefix(8))-\(hex.dropFirst(8).prefix(4))-\(hex.dropFirst(12).prefix(4))-\(hex.dropFirst(16).prefix(4))-\(hex.dropFirst(20).prefix(12))"
+    }
+}

service/Sources/App/Models/PostIDGenerator.swift

@@ -2,32 +2,32 @@ import Foundation
 
 enum PostIDGenerator {
     static func secretGenerator(from date: Date) -> UInt64 {
-        let formatter = DateFormatter()
-        formatter.dateFormat = "yyyyMMddHHmm"
-        let dateString = formatter.string(from: date)
-        let noise = UInt64(dateString) ?? 0
-        return noise
+        var calendar = Calendar(identifier: .gregorian)
+        calendar.timeZone = TimeZone(identifier: "UTC")!
+        let comps = calendar.dateComponents([.year, .month, .day, .hour, .minute], from: date)
+
+        let str = String(format: "%04d%02d%02d%02d%02d",
+                         comps.year!, comps.month!, comps.day!,
+                         comps.hour!, comps.minute!)
+        return UInt64(str) ?? 0
     }
 
     static func derivePostID(profileID: UUID, timestamp: Date, counter: UInt8) -> UUID {
         let noise = secretGenerator(from: timestamp)
         let combinedNoise = (noise << 8) | UInt64(counter)
-        var left = Array(profileID.uuidString.utf8)
-        var right = String(combinedNoise)
 
-        while right.count < 32 {
-            right.append("0")
-        }
+        var left = Array(profileID.uuidString.utf8.prefix(32))
+        while left.count < 32 { left.append(0) }
 
+        let right = String(format: "%032llu", combinedNoise)
         let center = Array(right.utf8.prefix(32))
-        while left.count < 32 {
-            left.append(0)
-        }
 
         let combined = zip(left, center).map { $0 ^ $1 }
-        let hex = combined.map { String(format: "%02x", $0) }.joined()
+        let hex = combined.map { hexLookup[Int($0)] }.joined()
         let uuidString = "\(hex.prefix(8))-\(hex.dropFirst(8).prefix(4))-\(hex.dropFirst(12).prefix(4))-\(hex.dropFirst(16).prefix(4))-\(hex.dropFirst(20).prefix(12))"
 
         return UUID(uuidString: uuidString) ?? UUID()
     }
+
+    private static let hexLookup: [String] = (0...255).map { String(format: "%02x", $0) }
 }