add caching for performance

AccessQueueService/Data/IAccessQueueRepo.cs

@@ -16,6 +16,6 @@ namespace AccessQueueService.Data
         public void Enqueue(AccessTicket ticket);
         public int DeleteExpiredTickets();
         public bool RemoveUser(string userId);
-        public bool DidDequeueUntilFull(int activeSeconds, int expirationSeconds, int capacityLimit);
+        public bool DidDequeueUntilFull(AccessQueueConfig config);
     }
 }

AccessQueueService/Data/TakeANumberAccessQueueRepo.cs

@@ -15,6 +15,9 @@ namespace AccessQueueService.Data
         internal ulong _nowServing = 0;
         internal ulong _nextUnusedTicket = 0;
 
+        private int? _cachedActiveUsers = null;
+        private DateTime _cachedActiveUsersTime = DateTime.MinValue;
+
         public int GetUnexpiredTicketsCount() => _accessTickets.Count(t => t.Value.ExpiresOn > DateTime.UtcNow);
         public int GetActiveTicketsCount(DateTime activeCutoff) => _accessTickets
             .Count(t => t.Value.ExpiresOn > DateTime.UtcNow && t.Value.LastActive > activeCutoff);
@@ -58,39 +61,53 @@ namespace AccessQueueService.Data
             return count;
         }
 
-        public bool DidDequeueUntilFull(int activeSeconds, int expirationSeconds, int capacityLimit)
+        public bool DidDequeueUntilFull(AccessQueueConfig config)
         {
             var now = DateTime.UtcNow;
-            var activeCutoff = now.AddSeconds(-activeSeconds);
+            var activeCutoff = now.AddSeconds(-config.ActivitySeconds.Value);
-            var numberOfActiveUsers = _accessTickets.Count(t => t.Value.ExpiresOn > now && t.Value.LastActive > activeCutoff);
+            if (config.CacheMilliseconds.HasValue && _cachedActiveUsers.HasValue && (now - _cachedActiveUsersTime).TotalMilliseconds < config.CacheMilliseconds)
-            var openSpots = capacityLimit - numberOfActiveUsers;
+            {
-            if (openSpots <= 0)
+                var numberOfActiveUsers = _cachedActiveUsers.Value;
+                var openSpots = config.CapacityLimit - numberOfActiveUsers;
+                if (openSpots <= 0)
+                {
+                    return true;
+                }
+            }
+            _cachedActiveUsers = _accessTickets.Count(t => t.Value.ExpiresOn > now && t.Value.LastActive > activeCutoff);
+            _cachedActiveUsersTime = now;
+            var openSpotsNew = config.CapacityLimit - _cachedActiveUsers;
+            if (openSpotsNew <= 0)
             {
                 return true;
             }
             int filledSpots = 0;
-            while (filledSpots < openSpots && _nowServing < _nextUnusedTicket)
+            while (filledSpots < openSpotsNew && _nowServing < _nextUnusedTicket)
             {
-                if (_accessQueue.TryRemove(_nowServing, out var nextUser))
+                if (_accessQueue.TryRemove(_nowServing++, out var nextUser))
                 {
                     _queueNumbers.TryRemove(nextUser.UserId, out _);
                     if (nextUser.LastActive < activeCutoff)
                     {
                         // User is inactive, throw away their ticket
-                        _nowServing++;
                         continue;
                     }
                     _accessTickets[nextUser.UserId] = new AccessTicket
                     {
                         UserId = nextUser.UserId,
-                        ExpiresOn = now.AddSeconds(expirationSeconds),
+                        ExpiresOn = now.AddSeconds(config.ExpirationSeconds.Value),
                         LastActive = now
                     };
                     filledSpots++;
                 }
-                _nowServing++;
             }
-            return filledSpots == openSpots;
+            // Invalidate cache if any users were granted access
+            if (filledSpots > 0)
+            {
+                _cachedActiveUsers = null;
+                _cachedActiveUsersTime = DateTime.MinValue;
+            }
+            return filledSpots == openSpotsNew;
         }
 
         public AccessTicket? GetTicket(string userId)
@@ -101,6 +118,8 @@ namespace AccessQueueService.Data
         public void UpsertTicket(AccessTicket ticket)
         {
             _accessTickets[ticket.UserId] = ticket;
+            _cachedActiveUsers = null;
+            _cachedActiveUsersTime = DateTime.MinValue;
         }
 
         public bool RemoveUser(string userId)

AccessQueueService/Models/AccessQueueConfig.cs

@@ -6,6 +6,7 @@ namespace AccessQueueService.Models
         public int? ActivitySeconds { get; set; }
         public int? ExpirationSeconds { get; set; }
         public bool? RollingExpiration { get; set; }
+        public int? CacheMilliseconds { get; set; }
 
         public AccessQueueConfig Clone()
         {

AccessQueueService/Services/AccessService.cs

@@ -23,7 +23,8 @@ namespace AccessQueueService.Services
                 ExpirationSeconds = _configuration.GetValue<int>("AccessQueue:ExpirationSeconds"),
                 ActivitySeconds = _configuration.GetValue<int>("AccessQueue:ActivitySeconds"),
                 CapacityLimit = _configuration.GetValue<int>("AccessQueue:CapacityLimit"),
-                RollingExpiration = _configuration.GetValue<bool>("AccessQueue:RollingExpiration")
+                RollingExpiration = _configuration.GetValue<bool>("AccessQueue:RollingExpiration"),
+                CacheMilliseconds = _configuration.GetValue<int>("AccessQueue:CacheMilliseconds")
             };
         }
         public AccessQueueConfig GetConfiguration() => _config.Clone();
@@ -53,10 +54,7 @@ namespace AccessQueueService.Services
             await _queueLock.WaitAsync();
             try
             {
-                var hasCapacity = !_accessQueueRepo.DidDequeueUntilFull(
+                var hasCapacity = !_accessQueueRepo.DidDequeueUntilFull(_config);
-                    _config.ActivitySeconds.Value,
-                    _config.ExpirationSeconds.Value,
-                    _config.CapacityLimit.Value);
                 var existingTicket = _accessQueueRepo.GetTicket(userId);
                 if (existingTicket != null && existingTicket.ExpiresOn > DateTime.UtcNow)
                 {
@@ -109,6 +107,10 @@ namespace AccessQueueService.Services
                         });
                         _logger.LogInformation("User {UserId} added to queue. Requests ahead: {RequestsAhead}.", userId, requestsAhead);
                     }
+                    else
+                    {
+                        _logger.LogInformation("User {UserId} already in queue. Requests ahead: {RequestsAhead}.", userId, requestsAhead);
+                    }
                     return new AccessResponse
                     {
                         ExpiresOn = null,

AccessQueueService/appsettings.json

@@ -23,14 +23,15 @@
       "Application": "AccessQueueService"
     }
   },
-    "AccessQueue": {
+  "AccessQueue": {
-        "CapacityLimit": 100,
+    "CapacityLimit": 100,
-        "ActivitySeconds": 900,
+    "ActivitySeconds": 900,
-        "ExpirationSeconds": 43200,
+    "ExpirationSeconds": 43200,
-        "RollingExpiration": true,
+    "RollingExpiration": true,
-        "CleanupIntervalSeconds": 60,
+    "CleanupIntervalSeconds": 60,
-        "BackupFilePath": "Logs\\backup.json",
+    "BackupFilePath": "Logs\\backup.json",
-        "BackupIntervalSeconds": 5
+    "BackupIntervalSeconds": 5,
-    },
+    "CacheMilliseconds": 1000
+  },
   "AllowedHosts": "*"
 }

AccessQueueServiceTests/AccessQueueRepoTests.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net.Sockets;
 using System.Text;
 using System.Text.Json;
 using System.Threading.Tasks;
@@ -14,12 +15,43 @@ namespace AccessQueueServiceTests
     public class AccessQueueRepoTests
     {
         private readonly TakeANumberAccessQueueRepo _repo;
+        private readonly AccessQueueConfig _simpleConfig = new()
+        {
+            ExpirationSeconds = 60,
+            ActivitySeconds = 60,
+            CapacityLimit = 1,
+            RollingExpiration = false,
+            CacheMilliseconds = null
+        };
+        private readonly AccessQueueConfig _configWithCache = new()
+        {
+            ExpirationSeconds = 60,
+            ActivitySeconds = 60,
+            CapacityLimit = 1,
+            RollingExpiration = false,
+            CacheMilliseconds = 100
+        };
+        private AccessQueueConfig SimpleConfigWithCapacity(int capacity) => new()
+        {
+            ExpirationSeconds = 60,
+            ActivitySeconds = 60,
+            CapacityLimit = capacity,
+            RollingExpiration = false,
+            CacheMilliseconds = null
+        };
 
         public AccessQueueRepoTests()
         {
             _repo = new TakeANumberAccessQueueRepo();
         }
 
+        private List<AccessTicket> GetSimpleTicketList() => new()
+        {
+            new() { UserId = "first", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow },
+            new() { UserId = "second", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow },
+            new() { UserId = "third", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow }
+        };
+
         [Fact]
         public void GetUnexpiredTicketsCount_ReturnsCorrectCount()
         {
@@ -91,7 +123,7 @@ namespace AccessQueueServiceTests
 
             var ticket = new AccessTicket { UserId = "a", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
             _repo.Enqueue(ticket);
-            bool result = _repo.DidDequeueUntilFull(60, 60, 1);
+            bool result = _repo.DidDequeueUntilFull(_simpleConfig);
             Assert.True(result);
             Assert.NotNull(_repo.GetTicket("a"));
         }
@@ -101,7 +133,7 @@ namespace AccessQueueServiceTests
         {
 
             _repo.UpsertTicket(new AccessTicket { UserId = "a", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow });
-            bool result = _repo.DidDequeueUntilFull(60, 60, 0);
+            bool result = _repo.DidDequeueUntilFull(SimpleConfigWithCapacity(0));
             Assert.True(result);
         }
 
@@ -155,7 +187,7 @@ namespace AccessQueueServiceTests
             var active = new AccessTicket { UserId = "active", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
             _repo.Enqueue(inactive);
             _repo.Enqueue(active);
-            bool result = _repo.DidDequeueUntilFull(5 * 60, 60, 1);
+            bool result = _repo.DidDequeueUntilFull(_simpleConfig);
             Assert.True(result);
             Assert.Null(_repo.GetTicket("inactive"));
             Assert.NotNull(_repo.GetTicket("active"));
@@ -164,12 +196,10 @@ namespace AccessQueueServiceTests
         [Fact]
         public void Enqueue_QueuesUsersInOrder()
         {
-            var ticket1 = new AccessTicket { UserId = "first", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow };
+            foreach (var ticket in GetSimpleTicketList())
-            var ticket2 = new AccessTicket { UserId = "second", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow };
+            {
-            var ticket3 = new AccessTicket { UserId = "third", ExpiresOn = DateTime.UtcNow, LastActive = DateTime.UtcNow };
+                _repo.Enqueue(ticket);
-            _repo.Enqueue(ticket1);
+            }
-            _repo.Enqueue(ticket2);
-            _repo.Enqueue(ticket3);
             Assert.Equal(0, _repo.GetRequestsAhead("first"));
             Assert.Equal(1, _repo.GetRequestsAhead("second"));
             Assert.Equal(2, _repo.GetRequestsAhead("third"));
@@ -178,14 +208,12 @@ namespace AccessQueueServiceTests
         [Fact]
         public void DidDequeueUntilFull_DequeuesUsersInOrder()
         {
-            var ticket1 = new AccessTicket { UserId = "first", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+            foreach (var ticket in GetSimpleTicketList())
-            var ticket2 = new AccessTicket { UserId = "second", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+            {
-            var ticket3 = new AccessTicket { UserId = "third", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+                _repo.Enqueue(ticket);
-            _repo.Enqueue(ticket1);
+            }
-            _repo.Enqueue(ticket2);
-            _repo.Enqueue(ticket3);
 
-            bool result = _repo.DidDequeueUntilFull(60 * 60, 60, 1);
+            bool result = _repo.DidDequeueUntilFull(_simpleConfig);
 
             Assert.True(result);
             Assert.NotNull(_repo.GetTicket("first"));
@@ -193,17 +221,33 @@ namespace AccessQueueServiceTests
             Assert.Null(_repo.GetTicket("third"));
         }
 
+        [Fact]
+        public void DidDequeuedUntilFull_CachesActiveTickets_WhenCacheMillisSet()
+        {
+            foreach (var ticket in GetSimpleTicketList())
+            {
+                _repo.Enqueue(ticket);
+            }
+
+            Assert.True(_repo.DidDequeueUntilFull(_configWithCache));
+            Assert.NotNull(_repo.GetTicket("first"));
+            Assert.Null(_repo.GetTicket("second"));
+            Assert.Null(_repo.GetTicket("third"));
+
+            Assert.True(_repo.DidDequeueUntilFull(_configWithCache));
+            Assert.Null(_repo.GetTicket("second"));
+            Assert.Null(_repo.GetTicket("third"));
+        }
+
         [Fact]
         public void Optimize_MaintainsQueueOrder()
         {
-            var ticket1 = new AccessTicket { UserId = "first", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+            foreach (var ticket in GetSimpleTicketList())
-            var ticket2 = new AccessTicket { UserId = "second", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+            {
-            var ticket3 = new AccessTicket { UserId = "third", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
+                _repo.Enqueue(ticket);
-            _repo.Enqueue(ticket1);
+            }
-            _repo.Enqueue(ticket2);
-            _repo.Enqueue(ticket3);
 
-            _repo.DidDequeueUntilFull(60 * 60, 60, 1);
+            _repo.DidDequeueUntilFull(_simpleConfig);
             _repo.Optimize();
 
             Assert.NotNull(_repo.GetTicket("first"));
@@ -211,7 +255,7 @@ namespace AccessQueueServiceTests
             Assert.Equal(1, _repo.GetRequestsAhead("third"));
             Assert.Equal(0ul, _repo._nowServing);
 
-            _repo.DidDequeueUntilFull(60 * 60, 60, 2);
+            _repo.DidDequeueUntilFull(SimpleConfigWithCapacity(2));
             Assert.NotNull(_repo.GetTicket("second"));
             Assert.Equal(0, _repo.GetRequestsAhead("third"));
         }
@@ -219,16 +263,13 @@ namespace AccessQueueServiceTests
         [Fact]
         public void Enqueue_MaintainsQueueOrder_WhenMaxValueExceeded()
         {
-            var ticket1 = new AccessTicket { UserId = "first", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
-            var ticket2 = new AccessTicket { UserId = "second", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
-            var ticket3 = new AccessTicket { UserId = "third", ExpiresOn = DateTime.UtcNow.AddMinutes(1), LastActive = DateTime.UtcNow };
-
             _repo._nowServing = long.MaxValue - 1;
             _repo._nextUnusedTicket = long.MaxValue - 1;
 
-            _repo.Enqueue(ticket1);
+            foreach (var ticket in GetSimpleTicketList())
-            _repo.Enqueue(ticket2);
+            {
-            _repo.Enqueue(ticket3);
+                _repo.Enqueue(ticket);
+            }
 
             Assert.Equal(0ul, _repo._nowServing);
             Assert.Equal(3ul, _repo._nextUnusedTicket);

AccessQueueServiceTests/AccessServiceTests.cs

@@ -16,6 +16,7 @@ namespace AccessQueueServiceTests
         const int ACT_MILLIS = 1000 * ACT_SECONDS;
         const int CAP_LIMIT = 5;
         const int BULK_COUNT = 10000;
+        const int CACHE_MILLIS = 1000;
         private readonly AccessService _accessService;
 
         public AccessServiceTests()
@@ -25,7 +26,8 @@ namespace AccessQueueServiceTests
                     { "AccessQueue:ExpirationSeconds", $"{EXP_SECONDS}" },
                     { "AccessQueue:ActivitySeconds", $"{ACT_SECONDS}" },
                     { "AccessQueue:CapacityLimit", $"{CAP_LIMIT}" },
-                    { "AccessQueue:RollingExpiration", "true" }
+                    { "AccessQueue:RollingExpiration", "true" },
+                    { "AccessQueue:CacheMilliseconds", $"{CACHE_MILLIS}" }
                 };
 
             var configuration = new ConfigurationBuilder()
@@ -87,9 +89,9 @@ namespace AccessQueueServiceTests
             Assert.NotNull(response);
             Assert.Null(response.ExpiresOn);
             Assert.True(response.RequestsAhead == CAP_LIMIT);
-            Assert.Equal(5, _accessService.UnexpiredTicketsCount);
+            Assert.Equal(CAP_LIMIT, _accessService.UnexpiredTicketsCount);
-            Assert.Equal(5, _accessService.ActiveTicketsCount);
+            Assert.Equal(CAP_LIMIT, _accessService.ActiveTicketsCount);
-            Assert.Equal(6, _accessService.QueueCount);
+            Assert.Equal(CAP_LIMIT + 1, _accessService.QueueCount);
         }