report a peer's port change locally without rewriting it

Keep IConfigurationManager source-compatible for plugin implementers.

Emby.Server.Implementations/AppBase/BaseConfigurationManager.cs

@@ -87,6 +87,12 @@ namespace Emby.Server.Implementations.AppBase
         /// <value>The application paths.</value>
         public IApplicationPaths CommonApplicationPaths { get; private set; }
 
+        /// <summary>
+        /// Gets or sets the bus announcing configuration writes to the other instances sharing this
+        /// configuration directory. Defaults to a no-op, which is the single-instance behaviour.
+        /// </summary>
+        public IConfigurationInvalidationBus InvalidationBus { get; set; } = NullConfigurationInvalidationBus.Instance;
+
         /// <summary>
         /// Gets or sets the system configuration.
         /// </summary>
@@ -169,6 +175,8 @@ namespace Emby.Server.Implementations.AppBase
             }
 
             OnConfigurationUpdated();
+
+            InvalidationBus.PublishLocalWrite(ConfigurationInvalidationScope.SystemConfiguration, null);
         }
 
         /// <summary>
@@ -350,6 +358,29 @@ namespace Emby.Server.Implementations.AppBase
             }
 
             OnNamedConfigurationUpdated(key, configuration);
+
+            InvalidationBus.PublishLocalWrite(ConfigurationInvalidationScope.NamedConfiguration, key);
+        }
+
+        /// <inheritdoc />
+        public void InvalidateCachedConfiguration(string? key)
+        {
+            if (string.IsNullOrEmpty(key))
+            {
+                lock (_configurationSyncLock)
+                {
+                    _configuration = null;
+                }
+
+                // Reloads the system configuration off the shared file as a side effect of re-deriving
+                // the cache path from it, then tells the in-process consumers to re-read it.
+                OnConfigurationUpdated();
+                return;
+            }
+
+            _configurations.TryRemove(key, out _);
+
+            OnNamedConfigurationUpdated(key, GetConfiguration(key));
         }
 
         /// <summary>

Emby.Server.Implementations/ApplicationHost.cs

@@ -706,6 +706,8 @@ namespace Emby.Server.Implementations
             BaseItem.UserDataManager = Resolve<IUserDataManager>();
             CollectionFolder.XmlSerializer = _xmlSerializer;
             CollectionFolder.ApplicationHost = this;
+            CollectionFolder.InvalidationBus = Resolve<IConfigurationInvalidationBus>();
+            ConfigurationManager.InvalidationBus = CollectionFolder.InvalidationBus;
             Folder.UserViewManager = Resolve<IUserViewManager>();
             Folder.CollectionManager = Resolve<ICollectionManager>();
             Folder.LimitedConcurrencyLibraryScheduler = Resolve<ILimitedConcurrencyLibraryScheduler>();
@@ -790,6 +792,43 @@ namespace Emby.Server.Implementations
             }
         }
 
+        /// <summary>
+        /// Works out what a configuration update means for the ports this process bound at startup.
+        /// </summary>
+        /// <param name="boundHttpPort">The HTTP port this process is bound to.</param>
+        /// <param name="boundHttpsPort">The HTTPS port this process is bound to.</param>
+        /// <param name="configuredHttpPort">The HTTP port the shared configuration now carries.</param>
+        /// <param name="configuredHttpsPort">The HTTPS port the shared configuration now carries.</param>
+        /// <param name="isPortAuthorized">Whether the shared configuration still marks the port as authorized.</param>
+        /// <param name="isApplyingRemoteInvalidation">Whether this update is another instance's write being applied.</param>
+        /// <returns>What the update requires of this instance.</returns>
+        internal static PortChangeOutcome EvaluatePortChange(
+            int boundHttpPort,
+            int boundHttpsPort,
+            int configuredHttpPort,
+            int configuredHttpsPort,
+            bool isPortAuthorized,
+            bool isApplyingRemoteInvalidation)
+        {
+            // Nothing is bound yet, so nothing has gone stale.
+            if (boundHttpPort == 0 || boundHttpsPort == 0)
+            {
+                return default;
+            }
+
+            if (configuredHttpPort == boundHttpPort && configuredHttpsPort == boundHttpsPort)
+            {
+                return default;
+            }
+
+            // Whoever wrote the change, this process is still listening on a port the configuration no
+            // longer names, so the pending restart is reported either way. The authorization flag belongs
+            // to the instance that made the change: it cleared the flag along with the port, and clearing
+            // it again here would write shared configuration on that instance's behalf and announce it a
+            // second time.
+            return new PortChangeOutcome(true, isPortAuthorized && !isApplyingRemoteInvalidation);
+        }
+
         /// <summary>
         /// Called when [configuration updated].
         /// </summary>
@@ -797,26 +836,24 @@ namespace Emby.Server.Implementations
         /// <param name="e">The <see cref="EventArgs"/> instance containing the event data.</param>
         private void OnConfigurationUpdated(object sender, EventArgs e)
         {
-            var requiresRestart = false;
             var networkConfiguration = ConfigurationManager.GetNetworkConfiguration();
 
-            // Don't do anything if these haven't been set yet
-            if (HttpPort != 0 && HttpsPort != 0)
-            {
-                // Need to restart if ports have changed
-                if (networkConfiguration.InternalHttpPort != HttpPort
-                    || networkConfiguration.InternalHttpsPort != HttpsPort)
-                {
-                    if (ConfigurationManager.Configuration.IsPortAuthorized)
-                    {
-                        ConfigurationManager.Configuration.IsPortAuthorized = false;
-                        ConfigurationManager.SaveConfiguration();
+            var portChange = EvaluatePortChange(
+                HttpPort,
+                HttpsPort,
+                networkConfiguration.InternalHttpPort,
+                networkConfiguration.InternalHttpsPort,
+                ConfigurationManager.Configuration.IsPortAuthorized,
+                ConfigurationInvalidationContext.IsApplyingRemoteInvalidation);
 
-                        requiresRestart = true;
-                    }
-                }
+            if (portChange.ClearsPortAuthorization)
+            {
+                ConfigurationManager.Configuration.IsPortAuthorized = false;
+                ConfigurationManager.SaveConfiguration();
             }
 
+            var requiresRestart = portChange.RequiresRestart;
+
             if (ValidateSslCertificate(networkConfiguration))
             {
                 requiresRestart = true;

Emby.Server.Implementations/Configuration/ConfigurationInvalidationSubscriber.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Controller.Entities;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+
+namespace Emby.Server.Implementations.Configuration
+{
+    /// <summary>
+    /// Applies the configuration invalidations published by the other instances sharing this
+    /// configuration directory, dropping the local cache entry so the next read comes off the shared file.
+    /// </summary>
+    public sealed class ConfigurationInvalidationSubscriber : IHostedService
+    {
+        private readonly IConfigurationInvalidationBus _bus;
+        private readonly IConfigurationManager _configurationManager;
+        private readonly ILogger<ConfigurationInvalidationSubscriber> _logger;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="ConfigurationInvalidationSubscriber"/> class.
+        /// </summary>
+        /// <param name="bus">The invalidation bus.</param>
+        /// <param name="configurationManager">The configuration manager holding the cached configuration.</param>
+        /// <param name="logger">The logger.</param>
+        public ConfigurationInvalidationSubscriber(
+            IConfigurationInvalidationBus bus,
+            IConfigurationManager configurationManager,
+            ILogger<ConfigurationInvalidationSubscriber> logger)
+        {
+            _bus = bus;
+            _configurationManager = configurationManager;
+            _logger = logger;
+        }
+
+        /// <inheritdoc />
+        public Task StartAsync(CancellationToken cancellationToken)
+        {
+            _bus.Subscribe(Apply);
+            return Task.CompletedTask;
+        }
+
+        /// <inheritdoc />
+        public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+
+        private void Apply(ConfigurationInvalidation invalidation)
+        {
+            try
+            {
+                // Applying re-raises the same update events a local save raises, so the in-process
+                // consumers re-read. The scope tells those consumers that the write was somebody else's,
+                // so the ones that answer an update by writing neither repeat it nor publish it back.
+                using var scope = ConfigurationInvalidationContext.BeginApply();
+
+                switch (invalidation.Scope)
+                {
+                    case ConfigurationInvalidationScope.SystemConfiguration:
+                        _configurationManager.InvalidateCachedConfiguration(null);
+                        break;
+                    case ConfigurationInvalidationScope.NamedConfiguration when !string.IsNullOrEmpty(invalidation.Target):
+                        _configurationManager.InvalidateCachedConfiguration(invalidation.Target);
+                        break;
+                    case ConfigurationInvalidationScope.LibraryOptions when !string.IsNullOrEmpty(invalidation.Target):
+                        CollectionFolder.InvalidateLibraryOptions(invalidation.Target);
+                        break;
+                    case ConfigurationInvalidationScope.AllLibraryOptions:
+                        CollectionFolder.InvalidateAllLibraryOptions();
+                        break;
+                    default:
+                        return;
+                }
+
+                _logger.LogDebug("Applied {Scope} invalidation for {Target} from {OriginId}.", invalidation.Scope, invalidation.Target, invalidation.OriginId);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to apply a {Scope} invalidation for {Target}.", invalidation.Scope, invalidation.Target);
+            }
+        }
+    }
+}

Emby.Server.Implementations/Configuration/RedisConfigurationInvalidationBus.cs

@@ -0,0 +1,96 @@
+using System;
+using System.Text.Json;
+using Jellyfin.Extensions.Json;
+using MediaBrowser.Common.Configuration;
+using Microsoft.Extensions.Logging;
+using StackExchange.Redis;
+
+namespace Emby.Server.Implementations.Configuration
+{
+    /// <summary>
+    /// A Redis pub/sub <see cref="IConfigurationInvalidationBus"/>. Notices are broadcast on one channel
+    /// and every instance but the publisher applies them.
+    /// </summary>
+    public sealed class RedisConfigurationInvalidationBus : IConfigurationInvalidationBus
+    {
+        private const string ChannelName = "jellyfin:configinvalidation";
+
+        private static readonly JsonSerializerOptions _jsonOptions = JsonDefaults.Options;
+
+        private readonly ISubscriber _subscriber;
+        private readonly ILogger<RedisConfigurationInvalidationBus> _logger;
+        private readonly string _originId;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RedisConfigurationInvalidationBus"/> class.
+        /// </summary>
+        /// <param name="redis">The Redis connection multiplexer.</param>
+        /// <param name="logger">The logger.</param>
+        public RedisConfigurationInvalidationBus(IConnectionMultiplexer redis, ILogger<RedisConfigurationInvalidationBus> logger)
+        {
+            ArgumentNullException.ThrowIfNull(redis);
+
+            _subscriber = redis.GetSubscriber();
+            _logger = logger;
+            _originId = Environment.GetEnvironmentVariable("JELLYFIN_INSTANCE_ID") ?? Environment.MachineName;
+        }
+
+        /// <inheritdoc />
+        public void Publish(ConfigurationInvalidationScope scope, string? target)
+        {
+            var invalidation = new ConfigurationInvalidation
+            {
+                Scope = scope,
+                Target = target,
+                OriginId = _originId
+            };
+
+            try
+            {
+                // Fire and forget: an admin saving configuration must never wait on, or fail because of,
+                // the bus. The write has already reached the shared directory by this point.
+                _subscriber.Publish(
+                    RedisChannel.Literal(ChannelName),
+                    JsonSerializer.Serialize(invalidation, _jsonOptions),
+                    CommandFlags.FireAndForget);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to publish {Scope} invalidation for {Target}; other instances keep their cached copy until they restart.", scope, target);
+            }
+        }
+
+        /// <inheritdoc />
+        public void Subscribe(Action<ConfigurationInvalidation> handler)
+        {
+            ArgumentNullException.ThrowIfNull(handler);
+
+            try
+            {
+                _subscriber.Subscribe(RedisChannel.Literal(ChannelName), (_, value) => Dispatch(handler, value));
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to subscribe to configuration invalidations; this instance keeps its cached configuration until it restarts.");
+            }
+        }
+
+        private void Dispatch(Action<ConfigurationInvalidation> handler, RedisValue value)
+        {
+            try
+            {
+                var invalidation = JsonSerializer.Deserialize<ConfigurationInvalidation>(value.ToString(), _jsonOptions);
+                if (invalidation is null || string.Equals(invalidation.OriginId, _originId, StringComparison.Ordinal))
+                {
+                    return;
+                }
+
+                handler(invalidation);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Failed to apply a configuration invalidation.");
+            }
+        }
+    }
+}

Emby.Server.Implementations/Library/LibraryManager.cs

@@ -2332,10 +2332,7 @@ namespace Emby.Server.Implementations.Library
         {
             IOrderedEnumerable<BaseItem>? orderedItems = null;
 
-            var comparers = sortBy.Select(o => GetComparer(o, user)).Where(c => c is not null).ToList();
-            items = PrefetchUserData(items, user, comparers);
-
-            foreach (var orderBy in comparers)
+            foreach (var orderBy in sortBy.Select(o => GetComparer(o, user)).Where(c => c is not null))
             {
                 if (orderBy is RandomComparer)
                 {
@@ -2367,14 +2364,14 @@ namespace Emby.Server.Implementations.Library
         {
             IOrderedEnumerable<BaseItem>? orderedItems = null;
 
-            var comparers = orderBy
-                .Select(o => (Comparer: GetComparer(o.OrderBy, user), o.SortOrder))
-                .Where(c => c.Comparer is not null)
-                .ToList();
-            items = PrefetchUserData(items, user, comparers.Select(c => c.Comparer).ToList());
-
-            foreach (var (comparer, sortOrder) in comparers)
+            foreach (var (name, sortOrder) in orderBy)
             {
+                var comparer = GetComparer(name, user);
+                if (comparer is null)
+                {
+                    continue;
+                }
+
                 if (comparer is RandomComparer)
                 {
                     var randomItems = items.ToArray();
@@ -2400,31 +2397,6 @@ namespace Emby.Server.Implementations.Library
             return orderedItems ?? items;
         }
 
-        // The user comparers read user data per item, so without one batched read up front an
-        // in-memory sort would issue a database round trip per comparison.
-        private IEnumerable<BaseItem> PrefetchUserData(IEnumerable<BaseItem> items, User? user, IReadOnlyList<IBaseItemComparer?> comparers)
-        {
-            if (user is null)
-            {
-                return items;
-            }
-
-            var userComparers = comparers.OfType<IUserBaseItemComparer>().ToList();
-            if (userComparers.Count == 0)
-            {
-                return items;
-            }
-
-            var itemList = items as IReadOnlyList<BaseItem> ?? items.ToList();
-            var userData = _userDataManager.GetUserDataBatch(itemList, user);
-            foreach (var comparer in userComparers)
-            {
-                comparer.PrefetchedUserData = userData;
-            }
-
-            return itemList;
-        }
-
         /// <summary>
         /// Gets the comparer.
         /// </summary>

Emby.Server.Implementations/Library/UserDataManager.cs

@@ -2,8 +2,10 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Linq;
 using System.Threading;
+using BitFaster.Caching.Lru;
 using Jellyfin.Database.Implementations;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Configuration;
@@ -25,6 +27,7 @@ namespace Emby.Server.Implementations.Library
     {
         private readonly IServerConfigurationManager _config;
         private readonly IDbContextFactory<JellyfinDbContext> _repository;
+        private readonly FastConcurrentLru<string, UserItemData> _cache;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="UserDataManager"/> class.
@@ -37,6 +40,7 @@ namespace Emby.Server.Implementations.Library
         {
             _config = config;
             _repository = repository;
+            _cache = new FastConcurrentLru<string, UserItemData>(Environment.ProcessorCount, _config.Configuration.CacheSize, StringComparer.OrdinalIgnoreCase);
         }
 
         /// <inheritdoc />
@@ -73,6 +77,11 @@ namespace Emby.Server.Implementations.Library
             dbContext.SaveChanges();
             transaction.Commit();
 
+            var userId = user.InternalId;
+            var cacheKey = GetCacheKey(userId, item.Id);
+            _cache.AddOrUpdate(cacheKey, userData);
+            item.UserData = dbContext.UserData.Where(e => e.ItemId == item.Id).AsNoTracking().ToArray(); // rehydrate the cached userdata
+
             UserDataSaved?.Invoke(this, new UserDataSaveEventArgs
             {
                 Keys = keys,
@@ -171,41 +180,64 @@ namespace Emby.Server.Implementations.Library
         /// <inheritdoc />
         public Dictionary<Guid, UserItemData> GetUserDataBatch(IReadOnlyList<BaseItem> items, User user)
         {
-            ArgumentNullException.ThrowIfNull(items);
-            ArgumentNullException.ThrowIfNull(user);
-
             var result = new Dictionary<Guid, UserItemData>(items.Count);
-            if (items.Count == 0)
+            var itemsNeedingQuery = new List<(BaseItem Item, List<string> Keys)>();
+
+            foreach (var item in items)
+            {
+                var cacheKey = GetCacheKey(user.InternalId, item.Id);
+                if (_cache.TryGet(cacheKey, out var cachedData))
+                {
+                    result[item.Id] = cachedData;
+                }
+                else
+                {
+                    var userDataRow = ResolveUserDataRow(item, item.UserData?.Where(e => e.UserId.Equals(user.Id)));
+                    var userData = userDataRow is not null ? Map(userDataRow) : null;
+                    if (userData is not null)
+                    {
+                        result[item.Id] = userData;
+                        _cache.AddOrUpdate(cacheKey, userData);
+                    }
+                    else
+                    {
+                        var keys = item.GetUserDataKeys();
+                        itemsNeedingQuery.Add((item, keys));
+                    }
+                }
+            }
+
+            if (itemsNeedingQuery.Count == 0)
             {
                 return result;
             }
 
-            // Fetch rows by item alone so rows kept under keys from older metadata resolve the same
-            // way as the single item path.
-            var itemIds = items.Select(e => e.Id).Distinct().ToList();
+            // Build a single query for all missing items. Fetch rows by item alone so rows kept
+            // under keys from older metadata resolve the same way as the in-memory path.
+            var allItemIds = itemsNeedingQuery.Select(x => x.Item.Id).ToList();
             using var context = _repository.CreateDbContext();
-            var userDataByItem = context.UserData
+            var userDataArray = context.UserData
                 .AsNoTracking()
                 .Where(e => e.UserId.Equals(user.Id))
-                .WhereOneOrMany(itemIds, e => e.ItemId)
-                .ToArray()
-                .GroupBy(e => e.ItemId)
-                .ToDictionary(g => g.Key, g => g.ToArray());
+                .WhereOneOrMany(allItemIds, e => e.ItemId)
+                .ToArray();
 
-            foreach (var item in items)
+            var userDataByItem = userDataArray.GroupBy(e => e.ItemId).ToDictionary(g => g.Key, g => g.ToArray());
+            foreach (var (item, keys) in itemsNeedingQuery)
             {
-                if (result.ContainsKey(item.Id))
+                UserItemData userData;
+                if (userDataByItem.TryGetValue(item.Id, out var itemUserData) && itemUserData.Length > 0)
                 {
-                    continue;
+                    userData = Map(ResolveUserDataRow(item, itemUserData)!);
+                }
+                else
+                {
+                    userData = new UserItemData { Key = keys.Count > 0 ? keys[0] : string.Empty };
                 }
 
-                var row = userDataByItem.TryGetValue(item.Id, out var itemUserData)
-                    ? ResolveUserDataRow(item, itemUserData)
-                    : null;
-
-                result[item.Id] = row is not null
-                    ? Map(row)
-                    : new UserItemData { Key = item.GetUserDataKeys().FirstOrDefault() ?? string.Empty };
+                result[item.Id] = userData;
+                var cacheKey = GetCacheKey(user.InternalId, item.Id);
+                _cache.AddOrUpdate(cacheKey, userData);
             }
 
             return result;
@@ -308,19 +340,20 @@ namespace Emby.Server.Implementations.Library
             return result;
         }
 
+        /// <summary>
+        /// Gets the internal key.
+        /// </summary>
+        /// <returns>System.String.</returns>
+        private static string GetCacheKey(long internalUserId, Guid itemId)
+        {
+            return internalUserId.ToString(CultureInfo.InvariantCulture) + "-" + itemId.ToString("N", CultureInfo.InvariantCulture);
+        }
+
         /// <inheritdoc />
         public UserItemData? GetUserData(User user, BaseItem item)
         {
             ArgumentNullException.ThrowIfNull(user);
-            ArgumentNullException.ThrowIfNull(item);
-
-            using var dbContext = _repository.CreateDbContext();
-            var rows = dbContext.UserData
-                .AsNoTracking()
-                .Where(e => e.ItemId == item.Id && e.UserId == user.Id)
-                .ToArray();
-
-            var row = ResolveUserDataRow(item, rows);
+            var row = ResolveUserDataRow(item, item.UserData?.Where(e => e.UserId.Equals(user.Id)));
             return row is not null ? Map(row) : new UserItemData()
             {
                 Key = item.GetUserDataKeys()[0],
@@ -503,6 +536,16 @@ namespace Emby.Server.Implementations.Library
             }
 
             dbContext.SaveChanges();
+
+            var cacheKey = GetCacheKey(user.InternalId, item.Id);
+            if (_cache.TryGet(cacheKey, out var cached))
+            {
+                cached.AudioStreamIndex = null;
+                cached.SubtitleStreamIndex = null;
+                _cache.AddOrUpdate(cacheKey, cached);
+            }
+
+            item.UserData = dbContext.UserData.Where(e => e.ItemId == item.Id).AsNoTracking().ToArray();
         }
     }
 }

Emby.Server.Implementations/PortChangeOutcome.cs

@@ -0,0 +1,14 @@
+namespace Emby.Server.Implementations
+{
+    /// <summary>
+    /// What a configuration update carrying different ports requires of the instance reading it.
+    /// </summary>
+    /// <param name="RequiresRestart">
+    /// Whether this process is still bound to a port the shared configuration no longer names, and so has
+    /// to report a pending restart.
+    /// </param>
+    /// <param name="ClearsPortAuthorization">
+    /// Whether this instance is the one that has to clear the port authorization flag and save it.
+    /// </param>
+    internal readonly record struct PortChangeOutcome(bool RequiresRestart, bool ClearsPortAuthorization);
+}

Emby.Server.Implementations/Sorting/DatePlayedComparer.cs

@@ -1,7 +1,6 @@
 #nullable disable
 
 using System;
-using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -28,12 +27,6 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
-        /// <summary>
-        /// Gets or sets the prefetched user data.
-        /// </summary>
-        /// <value>The prefetched user data.</value>
-        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
-
         /// <summary>
         /// Gets or sets the user data manager.
         /// </summary>
@@ -64,7 +57,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private DateTime GetDate(BaseItem x)
         {
-            var userdata = this.GetUserData(x);
+            var userdata = UserDataManager.GetUserData(User, x);
 
             if (userdata is not null && userdata.LastPlayedDate.HasValue)
             {

Emby.Server.Implementations/Sorting/IsFavoriteOrLikeComparer.cs

@@ -1,8 +1,6 @@
 #nullable disable
 #pragma warning disable CS1591
 
-using System;
-using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -37,12 +35,6 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
-        /// <summary>
-        /// Gets or sets the prefetched user data.
-        /// </summary>
-        /// <value>The prefetched user data.</value>
-        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
-
         /// <summary>
         /// Compares the specified x.
         /// </summary>
@@ -61,7 +53,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private int GetValue(BaseItem x)
         {
-            return x.IsFavoriteOrLiked(User, this.GetUserData(x)) ? 0 : 1;
+            return x.IsFavoriteOrLiked(User, userItemData: null) ? 0 : 1;
         }
     }
 }

Emby.Server.Implementations/Sorting/IsPlayedComparer.cs

@@ -2,8 +2,6 @@
 
 #pragma warning disable CS1591
 
-using System;
-using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -38,12 +36,6 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
-        /// <summary>
-        /// Gets or sets the prefetched user data.
-        /// </summary>
-        /// <value>The prefetched user data.</value>
-        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
-
         /// <summary>
         /// Compares the specified x.
         /// </summary>
@@ -62,7 +54,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private int GetValue(BaseItem x)
         {
-            return x.IsPlayed(User, this.GetUserData(x)) ? 0 : 1;
+            return x.IsPlayed(User, userItemData: null) ? 0 : 1;
         }
     }
 }

Emby.Server.Implementations/Sorting/IsUnplayedComparer.cs

@@ -2,8 +2,6 @@
 
 #pragma warning disable CS1591
 
-using System;
-using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -38,12 +36,6 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
-        /// <summary>
-        /// Gets or sets the prefetched user data.
-        /// </summary>
-        /// <value>The prefetched user data.</value>
-        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
-
         /// <summary>
         /// Compares the specified x.
         /// </summary>
@@ -62,7 +54,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private int GetValue(BaseItem x)
         {
-            return x.IsUnplayed(User, this.GetUserData(x)) ? 0 : 1;
+            return x.IsUnplayed(User, userItemData: null) ? 0 : 1;
         }
     }
 }

Emby.Server.Implementations/Sorting/PlayCountComparer.cs

@@ -1,7 +1,5 @@
 #nullable disable
 
-using System;
-using System.Collections.Generic;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using MediaBrowser.Controller.Entities;
@@ -40,12 +38,6 @@ namespace Emby.Server.Implementations.Sorting
         /// <value>The user manager.</value>
         public IUserManager UserManager { get; set; }
 
-        /// <summary>
-        /// Gets or sets the prefetched user data.
-        /// </summary>
-        /// <value>The prefetched user data.</value>
-        public IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData { get; set; }
-
         /// <summary>
         /// Compares the specified x.
         /// </summary>
@@ -64,7 +56,7 @@ namespace Emby.Server.Implementations.Sorting
         /// <returns>DateTime.</returns>
         private int GetValue(BaseItem x)
         {
-            var userdata = this.GetUserData(x);
+            var userdata = UserDataManager.GetUserData(User, x);
 
             return userdata is null ? 0 : userdata.PlayCount;
         }

Emby.Server.Implementations/TV/TVSeriesManager.cs

@@ -13,7 +13,6 @@ using MediaBrowser.Controller.Configuration;
 using MediaBrowser.Controller.Dto;
 using MediaBrowser.Controller.Entities;
 using MediaBrowser.Controller.Library;
-using MediaBrowser.Controller.Persistence;
 using MediaBrowser.Controller.TV;
 using MediaBrowser.Model.Querying;
 using Episode = MediaBrowser.Controller.Entities.TV.Episode;
@@ -125,100 +124,53 @@ namespace Emby.Server.Implementations.TV
 
             var batchResult = _libraryManager.GetNextUpEpisodesBatch(query, seriesKeys, includeSpecials, includeRewatching);
 
-            var results = new List<NextUpEpisodeBatchResult>(seriesKeys.Count);
+            var nextUpList = new List<(DateTime LastWatchedDate, Episode Episode)>();
+
             foreach (var seriesKey in seriesKeys)
             {
-                if (batchResult.TryGetValue(seriesKey, out var result))
+                if (!batchResult.TryGetValue(seriesKey, out var result))
                 {
-                    results.Add(result);
+                    continue;
                 }
-            }
 
-            // The selection below tests the played state of every episode it considers, so read the whole
-            // series batch in one query rather than one query per series.
-            var selectionCandidates = new List<BaseItem>();
-            foreach (var result in results)
-            {
-                AddCandidate(selectionCandidates, result.NextUp);
-                AddCandidate(selectionCandidates, result.LastWatched);
-                AddCandidate(selectionCandidates, result.NextPlayedForRewatching);
-                AddCandidate(selectionCandidates, result.LastWatchedForRewatching);
+                var nextEpisode = DetermineNextEpisode(result, user, includeSpecials, request.EnableResumable, false);
 
-                if (result.Specials is not null)
-                {
-                    selectionCandidates.AddRange(result.Specials);
-                }
-            }
-
-            var selectionUserData = _userDataManager.GetUserDataBatch(selectionCandidates, user);
-
-            var candidates = new List<NextUpCandidate>();
-            foreach (var result in results)
-            {
-                var nextEpisode = SelectNextEpisode(result, user, includeSpecials, includePlayed: false, selectionUserData);
                 if (nextEpisode is not null)
                 {
-                    candidates.Add(new NextUpCandidate(nextEpisode, result.LastWatched, !request.EnableResumable));
+                    // The last played date and the version that was actually played live on the version item's user data
+                    // The played state propagated to the sibling versions carries no date
+                    var (playedVersion, lastPlayedDate) = GetMostRecentlyPlayedVersion(result.LastWatched, user);
+                    nextEpisode = GetPreferredVersion(nextEpisode, result.LastWatched, playedVersion);
+
+                    DateTime lastWatchedDate = DateTime.MinValue;
+                    if (result.LastWatched is not null)
+                    {
+                        lastWatchedDate = lastPlayedDate ?? DateTime.MinValue.AddDays(1);
+                    }
+
+                    nextUpList.Add((lastWatchedDate, nextEpisode));
                 }
 
                 if (includeRewatching)
                 {
-                    var nextPlayedEpisode = SelectNextEpisode(result, user, includeSpecials, includePlayed: true, selectionUserData);
+                    var nextPlayedEpisode = DetermineNextEpisodeForRewatching(result, user, includeSpecials);
+
                     if (nextPlayedEpisode is not null)
                     {
-                        // A rewatch suggestion is dropped once it has been resumed, whatever the request asked for.
-                        candidates.Add(new NextUpCandidate(nextPlayedEpisode, result.LastWatchedForRewatching, true));
+                        var (playedVersion, lastPlayedDate) = GetMostRecentlyPlayedVersion(result.LastWatchedForRewatching, user);
+                        nextPlayedEpisode = GetPreferredVersion(nextPlayedEpisode, result.LastWatchedForRewatching, playedVersion);
+
+                        DateTime rewatchLastWatchedDate = DateTime.MinValue;
+                        if (result.LastWatchedForRewatching is not null)
+                        {
+                            rewatchLastWatchedDate = lastPlayedDate ?? DateTime.MinValue.AddDays(1);
+                        }
+
+                        nextUpList.Add((rewatchLastWatchedDate, nextPlayedEpisode));
                     }
                 }
             }
 
-            // The resume progress may live on an alternate version, so read every version in one query.
-            var episodeVersions = new List<BaseItem>();
-            foreach (var candidate in candidates)
-            {
-                if (candidate.DropWhenResumed)
-                {
-                    candidate.EpisodeVersions = candidate.Episode.GetAllVersions();
-                    episodeVersions.AddRange(candidate.EpisodeVersions);
-                }
-            }
-
-            if (episodeVersions.Count > 0)
-            {
-                var resumeUserData = _userDataManager.GetUserDataBatch(episodeVersions, user);
-                candidates.RemoveAll(candidate => candidate.EpisodeVersions
-                    .Any(version => GetUserData(user, version, resumeUserData)?.PlaybackPositionTicks > 0));
-            }
-
-            // The last played date and the version that was actually played live on the version item's user data
-            // The played state propagated to the sibling versions carries no date
-            var lastWatchedVersions = new List<BaseItem>();
-            foreach (var candidate in candidates)
-            {
-                if (candidate.LastWatched is Video lastWatchedVideo)
-                {
-                    candidate.LastWatchedVersions = lastWatchedVideo.GetAllVersions();
-                    lastWatchedVersions.AddRange(candidate.LastWatchedVersions);
-                }
-            }
-
-            var lastWatchedUserData = _userDataManager.GetUserDataBatch(lastWatchedVersions, user);
-
-            var nextUpList = new List<(DateTime LastWatchedDate, Episode Episode)>(candidates.Count);
-            foreach (var candidate in candidates)
-            {
-                var (playedVersion, lastPlayedDate) = GetMostRecentlyPlayedVersion(candidate.LastWatchedVersions, user, lastWatchedUserData);
-                var nextEpisode = GetPreferredVersion(candidate.Episode, candidate.LastWatched, playedVersion);
-
-                DateTime lastWatchedDate = DateTime.MinValue;
-                if (candidate.LastWatched is not null)
-                {
-                    lastWatchedDate = lastPlayedDate ?? DateTime.MinValue.AddDays(1);
-                }
-
-                nextUpList.Add((lastWatchedDate, nextEpisode));
-            }
-
             var sortedEpisodes = nextUpList
                 .OrderByDescending(x => x.LastWatchedDate)
                 .Select(x => (BaseItem)x.Episode);
@@ -226,25 +178,12 @@ namespace Emby.Server.Implementations.TV
             return GetResult(sortedEpisodes, request);
         }
 
-        private static void AddCandidate(List<BaseItem> candidates, BaseItem? item)
-        {
-            if (item is not null)
-            {
-                candidates.Add(item);
-            }
-        }
-
-        private UserItemData? GetUserData(User user, BaseItem item, IReadOnlyDictionary<Guid, UserItemData> prefetchedUserData)
-            => prefetchedUserData.TryGetValue(item.Id, out var userData)
-                ? userData
-                : _userDataManager.GetUserData(user, item);
-
-        private Episode? SelectNextEpisode(
-            NextUpEpisodeBatchResult result,
+        private Episode? DetermineNextEpisode(
+            MediaBrowser.Controller.Persistence.NextUpEpisodeBatchResult result,
             User user,
             bool includeSpecials,
-            bool includePlayed,
-            IReadOnlyDictionary<Guid, UserItemData> prefetchedUserData)
+            bool includeResumable,
+            bool includePlayed)
         {
             var nextEpisode = (includePlayed ? result.NextPlayedForRewatching : result.NextUp) as Episode;
             var lastWatchedEpisode = (includePlayed ? result.LastWatchedForRewatching : result.LastWatched) as Episode;
@@ -278,41 +217,60 @@ namespace Emby.Server.Implementations.TV
 
                     if (!includePlayed)
                     {
-                        sortedEpisodes = sortedEpisodes.Where(episode => GetUserData(user, episode, prefetchedUserData) is not { Played: true });
+                        sortedEpisodes = sortedEpisodes.Where(episode => _userDataManager.GetUserData(user, episode) is not { Played: true });
                     }
 
                     nextEpisode = sortedEpisodes.FirstOrDefault();
                 }
             }
 
+            if (nextEpisode is not null && !includeResumable)
+            {
+                // The resume progress may live on an alternate version
+                foreach (var version in nextEpisode.GetAllVersions())
+                {
+                    if (_userDataManager.GetUserData(user, version)?.PlaybackPositionTicks > 0)
+                    {
+                        return null;
+                    }
+                }
+            }
+
             return nextEpisode;
         }
 
+        private Episode? DetermineNextEpisodeForRewatching(
+            MediaBrowser.Controller.Persistence.NextUpEpisodeBatchResult result,
+            User user,
+            bool includeSpecials)
+        {
+            return DetermineNextEpisode(result, user, includeSpecials, includeResumable: false, includePlayed: true);
+        }
+
         /// <summary>
         /// Gets the version of the last watched episode that was actually played, together with its last played date.
         /// The version that was played carries the most recent LastPlayedDate.
         /// dates.
         /// </summary>
-        /// <param name="versions">The versions of the last watched episode.</param>
+        /// <param name="lastWatched">The last watched episode (any version).</param>
         /// <param name="user">The user.</param>
-        /// <param name="prefetchedUserData">User data read for every version up front.</param>
         /// <returns>The played version and its last played date.</returns>
-        private (Video? PlayedVersion, DateTime? LastPlayedDate) GetMostRecentlyPlayedVersion(
-            IReadOnlyList<Video> versions,
-            User user,
-            IReadOnlyDictionary<Guid, UserItemData> prefetchedUserData)
+        private (Video? PlayedVersion, DateTime? LastPlayedDate) GetMostRecentlyPlayedVersion(BaseItem? lastWatched, User user)
         {
-            if (versions.Count == 0)
+            if (lastWatched is not Video lastWatchedVideo)
             {
                 return (null, null);
             }
 
+            var versions = lastWatchedVideo.GetAllVersions();
+            var userDataByVersion = _userDataManager.GetUserDataBatch(versions, user);
+
             var playedVersion = VersionPlaybackSelector.SelectMostRecentlyPlayed(
                 versions,
-                version => GetUserData(user, version, prefetchedUserData),
+                version => userDataByVersion.GetValueOrDefault(version.Id),
                 data => data.LastPlayedDate.HasValue);
 
-            return (playedVersion, playedVersion is null ? null : GetUserData(user, playedVersion, prefetchedUserData)?.LastPlayedDate);
+            return (playedVersion, playedVersion is null ? null : userDataByVersion[playedVersion.Id].LastPlayedDate);
         }
 
         /// <summary>
@@ -388,28 +346,5 @@ namespace Emby.Server.Implementations.TV
                 totalCount,
                 items.ToArray());
         }
-
-        /// <summary>
-        /// An episode picked for Next Up, together with the versions its user data is read from.
-        /// </summary>
-        private sealed class NextUpCandidate
-        {
-            public NextUpCandidate(Episode episode, BaseItem? lastWatched, bool dropWhenResumed)
-            {
-                Episode = episode;
-                LastWatched = lastWatched;
-                DropWhenResumed = dropWhenResumed;
-            }
-
-            public Episode Episode { get; }
-
-            public BaseItem? LastWatched { get; }
-
-            public bool DropWhenResumed { get; }
-
-            public IReadOnlyList<Video> EpisodeVersions { get; set; } = [];
-
-            public IReadOnlyList<Video> LastWatchedVersions { get; set; } = [];
-        }
     }
 }

Jellyfin.Server/CoreAppHost.cs

@@ -112,6 +112,10 @@ namespace Jellyfin.Server
             // instance. Active by default once a Redis connection is configured, no-op otherwise.
             serviceCollection.AddScanLeaderLease(_startupConfig, Logger);
 
+            // Configuration invalidation bus: propagates shared-configuration and library-option writes
+            // to the other instances. Redis-backed when configured, no-op otherwise.
+            serviceCollection.AddConfigurationInvalidationBus(_startupConfig, Logger);
+
             foreach (var type in GetExportTypes<ILyricProvider>())
             {
                 serviceCollection.AddSingleton(typeof(ILyricProvider), type);

Jellyfin.Server/Extensions/ConfigurationInvalidationServiceCollectionExtensions.cs

@@ -0,0 +1,74 @@
+using System;
+using Emby.Server.Implementations.Configuration;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Controller.MediaEncoding;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+using StackExchange.Redis;
+
+namespace Jellyfin.Server.Extensions;
+
+/// <summary>
+/// Extensions for registering the shared-configuration invalidation bus.
+/// </summary>
+public static class ConfigurationInvalidationServiceCollectionExtensions
+{
+    /// <summary>
+    /// Registers the invalidation bus, Redis-backed when a connection string is configured and no-op
+    /// otherwise, and the subscriber applying the notices other instances publish.
+    /// </summary>
+    /// <remarks>
+    /// The connection string is only set for a multi-instance deployment, which is the only shape where
+    /// one instance can write the shared configuration directory behind another's back.
+    /// </remarks>
+    /// <param name="serviceCollection">The service collection.</param>
+    /// <param name="configuration">The configuration to read the Redis connection string from.</param>
+    /// <param name="logger">The logger to report the selected bus on.</param>
+    /// <returns>The updated service collection.</returns>
+    public static IServiceCollection AddConfigurationInvalidationBus(
+        this IServiceCollection serviceCollection,
+        IConfiguration configuration,
+        ILogger logger)
+    {
+        ArgumentNullException.ThrowIfNull(configuration);
+        ArgumentNullException.ThrowIfNull(logger);
+
+        if (string.IsNullOrEmpty(configuration[TranscodeStoreOptions.RedisConnectionStringKey]))
+        {
+            logger.LogInformation(
+                "Configuration invalidation bus: {Bus}. Shared-configuration and library-visibility changes stay local to the instance that made them; set {Key} to propagate them.",
+                nameof(NullConfigurationInvalidationBus),
+                TranscodeStoreOptions.RedisConnectionStringKey);
+
+            return serviceCollection.AddSingleton<IConfigurationInvalidationBus>(NullConfigurationInvalidationBus.Instance);
+        }
+
+        logger.LogInformation(
+            "Configuration invalidation bus: {Bus}. Shared-configuration and library-visibility changes propagate to every instance.",
+            nameof(RedisConfigurationInvalidationBus));
+
+        serviceCollection.AddSingleton<IConfigurationInvalidationBus>(sp =>
+        {
+            try
+            {
+                return new RedisConfigurationInvalidationBus(
+                    sp.GetRequiredService<IConnectionMultiplexer>(),
+                    sp.GetRequiredService<ILogger<RedisConfigurationInvalidationBus>>());
+            }
+            catch (Exception ex)
+            {
+                // Fail open: an unreachable Redis degrades to the single-instance behaviour of every
+                // instance keeping its own cached configuration, rather than aborting startup.
+                sp.GetRequiredService<ILogger<CoreAppHost>>().LogError(
+                    ex,
+                    "Redis is configured but unavailable, so shared-configuration changes will not propagate between instances. Check {Key}.",
+                    TranscodeStoreOptions.RedisConnectionStringKey);
+
+                return NullConfigurationInvalidationBus.Instance;
+            }
+        });
+
+        return serviceCollection.AddHostedService<ConfigurationInvalidationSubscriber>();
+    }
+}

MediaBrowser.Common/Configuration/ConfigurationInvalidation.cs

@@ -0,0 +1,26 @@
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// A notice that one instance has written shared configuration, so every other instance has to drop
+    /// its locally cached copy and read the shared file again.
+    /// </summary>
+    public sealed class ConfigurationInvalidation
+    {
+        /// <summary>
+        /// Gets or sets the cache this notice refers to.
+        /// </summary>
+        public ConfigurationInvalidationScope Scope { get; set; }
+
+        /// <summary>
+        /// Gets or sets what was invalidated within the scope: the configuration key for
+        /// <see cref="ConfigurationInvalidationScope.NamedConfiguration"/>, the library path for
+        /// <see cref="ConfigurationInvalidationScope.LibraryOptions"/>, and <c>null</c> otherwise.
+        /// </summary>
+        public string? Target { get; set; }
+
+        /// <summary>
+        /// Gets or sets the identity of the instance that published the notice, so it can ignore its own.
+        /// </summary>
+        public string? OriginId { get; set; }
+    }
+}

MediaBrowser.Common/Configuration/ConfigurationInvalidationBusExtensions.cs

@@ -0,0 +1,30 @@
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// Extensions for <see cref="IConfigurationInvalidationBus"/>.
+    /// </summary>
+    public static class ConfigurationInvalidationBusExtensions
+    {
+        /// <summary>
+        /// Announces a write this instance originated, and stays silent for a write induced by an
+        /// invalidation another instance published.
+        /// </summary>
+        /// <remarks>
+        /// This is the backstop for the write path: a consumer reacting to an applied invalidation by
+        /// writing - including a plugin that knows nothing about the bus - cannot turn that write into a
+        /// notice of its own.
+        /// </remarks>
+        /// <param name="bus">The bus.</param>
+        /// <param name="scope">The cache that was written.</param>
+        /// <param name="target">The configuration key or library path that was written, if any.</param>
+        public static void PublishLocalWrite(this IConfigurationInvalidationBus bus, ConfigurationInvalidationScope scope, string? target)
+        {
+            if (ConfigurationInvalidationContext.IsApplyingRemoteInvalidation)
+            {
+                return;
+            }
+
+            bus.Publish(scope, target);
+        }
+    }
+}

MediaBrowser.Common/Configuration/ConfigurationInvalidationContext.cs

@@ -0,0 +1,57 @@
+using System;
+using System.Threading;
+
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// Marks the flow of control that is applying an invalidation published by another instance, so the
+    /// reactions to it can tell a remote write apart from a local one.
+    /// </summary>
+    /// <remarks>
+    /// Applying an invalidation raises the same update events a local save raises, because the in-process
+    /// consumers have to re-read the configuration either way. Some of those consumers answer an update by
+    /// writing, and that write must neither repeat what the publishing instance already did nor fan back
+    /// out over the bus. The flag rides the execution context, so it reaches the queued and asynchronous
+    /// event handlers as well as the synchronous ones.
+    /// </remarks>
+    public static class ConfigurationInvalidationContext
+    {
+        private static readonly AsyncLocal<bool> _applyingRemoteInvalidation = new();
+
+        /// <summary>
+        /// Gets a value indicating whether the current flow of control is applying an invalidation
+        /// published by another instance rather than handling a local save.
+        /// </summary>
+        public static bool IsApplyingRemoteInvalidation => _applyingRemoteInvalidation.Value;
+
+        /// <summary>
+        /// Marks the current flow of control as applying a remote invalidation until the returned scope is
+        /// disposed.
+        /// </summary>
+        /// <returns>The scope to dispose once the invalidation has been applied.</returns>
+        public static IDisposable BeginApply() => new ApplyScope();
+
+        private sealed class ApplyScope : IDisposable
+        {
+            private readonly bool _previous;
+            private bool _disposed;
+
+            public ApplyScope()
+            {
+                _previous = _applyingRemoteInvalidation.Value;
+                _applyingRemoteInvalidation.Value = true;
+            }
+
+            public void Dispose()
+            {
+                if (_disposed)
+                {
+                    return;
+                }
+
+                _disposed = true;
+                _applyingRemoteInvalidation.Value = _previous;
+            }
+        }
+    }
+}

MediaBrowser.Common/Configuration/ConfigurationInvalidationScope.cs

@@ -0,0 +1,29 @@
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// Identifies which locally cached copy of the shared configuration a
+    /// <see cref="ConfigurationInvalidation"/> refers to.
+    /// </summary>
+    public enum ConfigurationInvalidationScope
+    {
+        /// <summary>
+        /// The system configuration cached by the configuration manager.
+        /// </summary>
+        SystemConfiguration = 0,
+
+        /// <summary>
+        /// A single named configuration, identified by its key.
+        /// </summary>
+        NamedConfiguration = 1,
+
+        /// <summary>
+        /// The library options of a single collection folder, identified by its path.
+        /// </summary>
+        LibraryOptions = 2,
+
+        /// <summary>
+        /// The library options of every collection folder, for changes to the library structure itself.
+        /// </summary>
+        AllLibraryOptions = 3
+    }
+}

MediaBrowser.Common/Configuration/IConfigurationInvalidationBus.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// Carries cache-invalidation notices between the instances that share one configuration directory.
+    /// </summary>
+    /// <remarks>
+    /// The shared directory carries the content; this bus only carries the fact that it changed. Every
+    /// implementation is expected to fail open: a bus that cannot deliver must not throw into the write
+    /// path, leaving each instance on its own locally cached copy until it restarts.
+    /// </remarks>
+    public interface IConfigurationInvalidationBus
+    {
+        /// <summary>
+        /// Announces that this instance has written shared configuration.
+        /// </summary>
+        /// <param name="scope">The cache that was written.</param>
+        /// <param name="target">The configuration key or library path that was written, if any.</param>
+        void Publish(ConfigurationInvalidationScope scope, string? target);
+
+        /// <summary>
+        /// Registers the handler invoked for notices published by other instances.
+        /// </summary>
+        /// <param name="handler">The handler applying the invalidation locally.</param>
+        void Subscribe(Action<ConfigurationInvalidation> handler);
+    }
+}

MediaBrowser.Common/Configuration/IConfigurationManager.cs

@@ -85,6 +85,20 @@ namespace MediaBrowser.Common.Configuration
         /// </summary>
         /// <param name="factories">The factories.</param>
         void AddParts(IEnumerable<IConfigurationFactory> factories);
+
+        /// <summary>
+        /// Drops the locally cached copy of configuration another instance has written to the shared
+        /// configuration directory, so the next read reloads it, and raises the local update event.
+        /// </summary>
+        /// <remarks>
+        /// An implementation predating the invalidation bus keeps the default, which reports that it
+        /// cannot drop its cache rather than quietly leaving it stale. The caller applying a remote
+        /// notice treats that as a failed apply and logs it.
+        /// </remarks>
+        /// <param name="key">The named configuration key, or <c>null</c> for the system configuration.</param>
+        /// <exception cref="NotSupportedException">The implementation cannot drop its cached configuration.</exception>
+        void InvalidateCachedConfiguration(string? key)
+            => throw new NotSupportedException(GetType().Name + " cannot drop configuration cached from the shared configuration directory, so writes by other instances will not be picked up.");
     }
 
     public static class ConfigurationManagerExtensions

MediaBrowser.Common/Configuration/NullConfigurationInvalidationBus.cs

@@ -0,0 +1,27 @@
+using System;
+
+namespace MediaBrowser.Common.Configuration
+{
+    /// <summary>
+    /// A no-op <see cref="IConfigurationInvalidationBus"/> used by single-instance installs and whenever
+    /// the shared bus is unavailable. Every instance keeps its own cached configuration, which is the
+    /// behaviour of an install that has only one.
+    /// </summary>
+    public sealed class NullConfigurationInvalidationBus : IConfigurationInvalidationBus
+    {
+        /// <summary>
+        /// Gets the shared instance.
+        /// </summary>
+        public static NullConfigurationInvalidationBus Instance { get; } = new NullConfigurationInvalidationBus();
+
+        /// <inheritdoc />
+        public void Publish(ConfigurationInvalidationScope scope, string? target)
+        {
+        }
+
+        /// <inheritdoc />
+        public void Subscribe(Action<ConfigurationInvalidation> handler)
+        {
+        }
+    }
+}

MediaBrowser.Controller/Entities/CollectionFolder.cs

@@ -14,6 +14,7 @@ using System.Threading.Tasks;
 using Jellyfin.Data.Enums;
 using Jellyfin.Database.Implementations.Entities;
 using Jellyfin.Extensions.Json;
+using MediaBrowser.Common.Configuration;
 using MediaBrowser.Controller.IO;
 using MediaBrowser.Controller.Library;
 using MediaBrowser.Controller.Providers;
@@ -70,6 +71,12 @@ namespace MediaBrowser.Controller.Entities
 
         public static IServerApplicationHost ApplicationHost { get; set; }
 
+        /// <summary>
+        /// Gets or sets the bus announcing library option writes to the other instances sharing this
+        /// configuration directory. Defaults to a no-op, which is the single-instance behaviour.
+        /// </summary>
+        public static IConfigurationInvalidationBus InvalidationBus { get; set; } = NullConfigurationInvalidationBus.Instance;
+
         [JsonIgnore]
         public override bool SupportsPlayedStatus => false;
 
@@ -188,11 +195,36 @@ namespace MediaBrowser.Controller.Entities
             XmlSerializer.SerializeToFile(clone, GetLibraryOptionsPath(path));
 
             LibraryOptionsUpdated?.Invoke(null, new LibraryOptionsUpdatedEventArgs(path, options));
+
+            InvalidationBus.PublishLocalWrite(ConfigurationInvalidationScope.LibraryOptions, path);
         }
 
-        public static void OnCollectionFolderChange()
+        /// <summary>
+        /// Drops the cached options of one library so the next read comes off <c>options.xml</c> again.
+        /// Applied on the instances that did not write, and so does not publish.
+        /// </summary>
+        /// <param name="path">The library path.</param>
+        public static void InvalidateLibraryOptions(string path)
+        {
+            _libraryOptions.TryRemove(path, out _);
+
+            LibraryOptionsUpdated?.Invoke(null, new LibraryOptionsUpdatedEventArgs(path, GetLibraryOptions(path)));
+        }
+
+        /// <summary>
+        /// Drops every cached library option set. Applied on the instances that did not write, and so does
+        /// not publish.
+        /// </summary>
+        public static void InvalidateAllLibraryOptions()
             => _libraryOptions.Clear();
 
+        public static void OnCollectionFolderChange()
+        {
+            InvalidateAllLibraryOptions();
+
+            InvalidationBus.PublishLocalWrite(ConfigurationInvalidationScope.AllLibraryOptions, null);
+        }
+
         public override bool IsSaveLocalMetadataEnabled()
         {
             return true;

MediaBrowser.Controller/Entities/UserViewBuilder.cs

@@ -449,26 +449,19 @@ namespace MediaBrowser.Controller.Entities
             IUserDataManager userDataManager,
             ILibraryManager libraryManager)
         {
-            var itemList = items as IReadOnlyList<BaseItem> ?? items.ToList();
-
-            // The user data checks below run per item, so read them all in one query up front.
-            var userDataBatch = user is not null && RequiresUserData(query)
-                ? userDataManager.GetUserDataBatch(itemList, user)
-                : null;
-
-            var filtered = itemList.Where(i => Filter(i, user, query, userDataManager, libraryManager, userDataBatch));
+            var filtered = items.Where(i => Filter(i, user, query, userDataManager, libraryManager));
 
             if (query.IsPlayed.HasValue && user is not null)
             {
-                var filteredList = filtered.ToList();
-                var folderIds = filteredList.OfType<Folder>().Select(f => f.Id).ToList();
+                var itemList = filtered.ToList();
+                var folderIds = itemList.OfType<Folder>().Select(f => f.Id).ToList();
 
                 if (folderIds.Count > 0)
                 {
                     var counts = libraryManager.GetPlayedAndTotalCountBatch(folderIds, user);
                     var isPlayedValue = query.IsPlayed.Value;
 
-                    return filteredList.Where(item =>
+                    return itemList.Where(item =>
                     {
                         if (item is Folder)
                         {
@@ -480,7 +473,7 @@ namespace MediaBrowser.Controller.Entities
                     });
                 }
 
-                return filteredList;
+                return itemList;
             }
 
             return filtered;
@@ -522,29 +515,12 @@ namespace MediaBrowser.Controller.Entities
                 itemsArray);
         }
 
-        private static bool RequiresUserData(InternalItemsQuery query)
-            => query.IsLiked.HasValue
-                || query.IsFavoriteOrLiked.HasValue
-                || query.IsFavorite.HasValue
-                || query.IsResumable.HasValue
-                || query.IsPlayed.HasValue;
-
-        private static UserItemData GetUserData(
-            IUserDataManager userDataManager,
-            User user,
-            BaseItem item,
-            Dictionary<Guid, UserItemData> userDataBatch)
-            => userDataBatch is not null && userDataBatch.TryGetValue(item.Id, out var userData)
-                ? userData
-                : userDataManager.GetUserData(user, item);
-
         private static bool Filter(
             BaseItem item,
             User user,
             InternalItemsQuery query,
             IUserDataManager userDataManager,
-            ILibraryManager libraryManager,
-            Dictionary<Guid, UserItemData> userDataBatch)
+            ILibraryManager libraryManager)
         {
             if (!string.IsNullOrEmpty(query.NameStartsWith) && !item.SortName.StartsWith(query.NameStartsWith, StringComparison.InvariantCultureIgnoreCase))
             {
@@ -592,7 +568,7 @@ namespace MediaBrowser.Controller.Entities
 
             if (query.IsLiked.HasValue)
             {
-                userData = GetUserData(userDataManager, user, item, userDataBatch);
+                userData = userDataManager.GetUserData(user, item);
                 if (!userData.Likes.HasValue || userData.Likes != query.IsLiked.Value)
                 {
                     return false;
@@ -601,7 +577,7 @@ namespace MediaBrowser.Controller.Entities
 
             if (query.IsFavoriteOrLiked.HasValue)
             {
-                userData ??= GetUserData(userDataManager, user, item, userDataBatch);
+                userData ??= userDataManager.GetUserData(user, item);
                 var isFavoriteOrLiked = userData.IsFavorite || (userData.Likes ?? false);
 
                 if (isFavoriteOrLiked != query.IsFavoriteOrLiked.Value)
@@ -612,7 +588,7 @@ namespace MediaBrowser.Controller.Entities
 
             if (query.IsFavorite.HasValue)
             {
-                userData ??= GetUserData(userDataManager, user, item, userDataBatch);
+                userData ??= userDataManager.GetUserData(user, item);
                 if (userData.IsFavorite != query.IsFavorite.Value)
                 {
                     return false;
@@ -621,7 +597,7 @@ namespace MediaBrowser.Controller.Entities
 
             if (query.IsResumable.HasValue)
             {
-                userData ??= GetUserData(userDataManager, user, item, userDataBatch);
+                userData ??= userDataManager.GetUserData(user, item);
                 var isResumable = userData.PlaybackPositionTicks > 0;
 
                 if (isResumable != query.IsResumable.Value)
@@ -636,7 +612,7 @@ namespace MediaBrowser.Controller.Entities
                 // Folders are batch-filtered by the collection Filter() overload.
                 if (!item.IsFolder)
                 {
-                    userData ??= GetUserData(userDataManager, user, item, userDataBatch);
+                    userData ??= userDataManager.GetUserData(user, item);
                     if (item.IsPlayed(user, userData) != query.IsPlayed.Value)
                     {
                         return false;

MediaBrowser.Controller/Sorting/IUserBaseItemComparer.cs

@@ -1,9 +1,6 @@
 #nullable disable
 
-using System;
-using System.Collections.Generic;
 using Jellyfin.Database.Implementations.Entities;
-using MediaBrowser.Controller.Entities;
 using MediaBrowser.Controller.Library;
 
 namespace MediaBrowser.Controller.Sorting
@@ -30,16 +27,5 @@ namespace MediaBrowser.Controller.Sorting
         /// </summary>
         /// <value>The user data repository.</value>
         IUserDataManager UserDataManager { get; set; }
-
-        /// <summary>
-        /// Gets or sets user data for the items being sorted, keyed by item id, read once up front.
-        /// A comparer that does not store it reads its user data one item at a time instead.
-        /// </summary>
-        /// <value>The prefetched user data, or <c>null</c> when none was prefetched.</value>
-        IReadOnlyDictionary<Guid, UserItemData> PrefetchedUserData
-        {
-            get => null;
-            set { }
-        }
     }
 }

MediaBrowser.Controller/Sorting/UserBaseItemComparerExtensions.cs

@@ -1,28 +0,0 @@
-#nullable disable
-
-using MediaBrowser.Controller.Entities;
-
-namespace MediaBrowser.Controller.Sorting
-{
-    /// <summary>
-    /// Helpers shared by the comparers that sort on user data.
-    /// </summary>
-    public static class UserBaseItemComparerExtensions
-    {
-        /// <summary>
-        /// Gets the user data for an item, preferring the batch the sort prefetched.
-        /// </summary>
-        /// <param name="comparer">The comparer.</param>
-        /// <param name="item">The item.</param>
-        /// <returns>The item's user data.</returns>
-        public static UserItemData GetUserData(this IUserBaseItemComparer comparer, BaseItem item)
-        {
-            if (comparer.PrefetchedUserData is not null && comparer.PrefetchedUserData.TryGetValue(item.Id, out var userData))
-            {
-                return userData;
-            }
-
-            return comparer.UserDataManager.GetUserData(comparer.User, item);
-        }
-    }
-}

src/Jellyfin.LiveTv/Channels/ChannelManager.cs

@@ -212,8 +212,7 @@ namespace Jellyfin.LiveTv.Channels
             if (query.IsFavorite.HasValue)
             {
                 var val = query.IsFavorite.Value;
-                var userData = _userDataManager.GetUserDataBatch(channels, user);
-                channels = channels.Where(i => userData.TryGetValue(i.Id, out var data) && data.IsFavorite == val)
+                channels = channels.Where(i => _userDataManager.GetUserData(user, i).IsFavorite == val)
                     .ToList();
             }
 

src/Jellyfin.LiveTv/LiveTvManager.cs

@@ -304,17 +304,8 @@ namespace Jellyfin.LiveTv
 
             if (query.IsAiring ?? false)
             {
-                // Scoring reads the channel's user data per program, so read every channel's in one query.
-                var channels = programList
-                    .Cast<LiveTvProgram>()
-                    .Select(i => _libraryManager.GetItemById(i.ChannelId))
-                    .OfType<BaseItem>()
-                    .DistinctBy(i => i.Id)
-                    .ToList();
-                var channelUserData = _userDataManager.GetUserDataBatch(channels, user);
-
                 orderedPrograms = orderedPrograms
-                    .ThenByDescending(i => GetRecommendationScore(i, user, true, channelUserData));
+                    .ThenByDescending(i => GetRecommendationScore(i, user, true));
             }
 
             IEnumerable<BaseItem> programs = orderedPrograms;
@@ -347,11 +338,7 @@ namespace Jellyfin.LiveTv
                 _dtoService.GetBaseItemDtos(internalResult.Items, options, query.User)));
         }
 
-        private int GetRecommendationScore(
-            LiveTvProgram program,
-            User user,
-            bool factorChannelWatchCount,
-            IReadOnlyDictionary<Guid, UserItemData> channelUserData)
+        private int GetRecommendationScore(LiveTvProgram program, User user, bool factorChannelWatchCount)
         {
             var score = 0;
 
@@ -372,9 +359,7 @@ namespace Jellyfin.LiveTv
                 return score;
             }
 
-            var channelUserdata = channelUserData.TryGetValue(channel.Id, out var cached)
-                ? cached
-                : _userDataManager.GetUserData(user, channel);
+            var channelUserdata = _userDataManager.GetUserData(user, channel);
 
             if (channelUserdata.Likes.HasValue)
             {

src/Jellyfin.LiveTv/Recordings/RecordingsManager.cs

@@ -444,6 +444,13 @@ public sealed class RecordingsManager : IRecordingsManager, IDisposable
 
     private async void OnNamedConfigurationUpdated(object? sender, ConfigurationUpdateEventArgs e)
     {
+        // The instance that wrote the change creates the folders; racing it from here would write the
+        // same virtual folder a second time.
+        if (ConfigurationInvalidationContext.IsApplyingRemoteInvalidation)
+        {
+            return;
+        }
+
         if (string.Equals(e.Key, "livetv", StringComparison.OrdinalIgnoreCase))
         {
             await CreateRecordingFolders().ConfigureAwait(false);

tests/Jellyfin.Server.Implementations.Tests/Configuration/ApplicationHostPortChangeTests.cs

@@ -0,0 +1,81 @@
+using Emby.Server.Implementations;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// The decision <c>ApplicationHost.OnConfigurationUpdated</c> makes about a port change. The ports this
+/// process bound are fixed for its lifetime and the pending-restart flag is per-process, so an instance
+/// applying another instance's port change still has to notice its own binding went stale - while leaving
+/// the authorization write, and the notice that follows it, to the instance that made the change.
+/// </summary>
+public static class ApplicationHostPortChangeTests
+{
+    /// <summary>
+    /// The local case, unchanged: clear the authorization flag and report the pending restart.
+    /// </summary>
+    [Fact]
+    public static void LocalPortChange_ClearsAuthorizationAndRequiresRestart()
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(8096, 8920, 9096, 8920, true, false);
+
+        Assert.True(outcome.RequiresRestart);
+        Assert.True(outcome.ClearsPortAuthorization);
+    }
+
+    /// <summary>
+    /// The cross-instance case: the peer wrote the new port and cleared the flag with it, so this
+    /// instance must not write, but it is still listening on the old port and has to say so.
+    /// </summary>
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public static void RemotePortChange_RequiresRestartWithoutWriting(bool isPortAuthorized)
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(8096, 8920, 9096, 8920, isPortAuthorized, true);
+
+        Assert.True(outcome.RequiresRestart);
+        Assert.False(outcome.ClearsPortAuthorization);
+    }
+
+    /// <summary>
+    /// A second update while a port change is already pending must not write the flag again, and the
+    /// binding is still stale.
+    /// </summary>
+    [Fact]
+    public static void LocalPortChange_WithAuthorizationAlreadyCleared_RequiresRestartWithoutWriting()
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(8096, 8920, 9096, 8920, false, false);
+
+        Assert.True(outcome.RequiresRestart);
+        Assert.False(outcome.ClearsPortAuthorization);
+    }
+
+    /// <summary>
+    /// An update that leaves the ports alone is not a port change, whoever wrote it.
+    /// </summary>
+    [Theory]
+    [InlineData(false)]
+    [InlineData(true)]
+    public static void UnchangedPorts_DoNothing(bool isApplyingRemoteInvalidation)
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(8096, 8920, 8096, 8920, true, isApplyingRemoteInvalidation);
+
+        Assert.False(outcome.RequiresRestart);
+        Assert.False(outcome.ClearsPortAuthorization);
+    }
+
+    /// <summary>
+    /// Nothing is decided before the ports have been bound.
+    /// </summary>
+    [Theory]
+    [InlineData(0, 8920)]
+    [InlineData(8096, 0)]
+    public static void UnboundPorts_DoNothing(int boundHttpPort, int boundHttpsPort)
+    {
+        var outcome = ApplicationHost.EvaluatePortChange(boundHttpPort, boundHttpsPort, 9096, 9920, true, false);
+
+        Assert.False(outcome.RequiresRestart);
+        Assert.False(outcome.ClearsPortAuthorization);
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/FakeInvalidationBusFabric.cs

@@ -0,0 +1,73 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using MediaBrowser.Common.Configuration;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// An in-process stand-in for the Redis pub/sub bus: every endpoint connected to one fabric receives
+/// what the others publish, and never its own notices.
+/// </summary>
+internal sealed class FakeInvalidationBusFabric
+{
+    private readonly List<Endpoint> _endpoints = new();
+
+    /// <summary>
+    /// Connects a new instance to the fabric.
+    /// </summary>
+    /// <param name="originId">The identity of the connecting instance.</param>
+    /// <returns>The bus of that instance.</returns>
+    public IConfigurationInvalidationBus Connect(string originId)
+    {
+        var endpoint = new Endpoint(this, originId);
+        lock (_endpoints)
+        {
+            _endpoints.Add(endpoint);
+        }
+
+        return endpoint;
+    }
+
+    private void Broadcast(ConfigurationInvalidation invalidation)
+    {
+        Endpoint[] endpoints;
+        lock (_endpoints)
+        {
+            endpoints = _endpoints.ToArray();
+        }
+
+        foreach (var endpoint in endpoints.Where(e => !string.Equals(e.OriginId, invalidation.OriginId, StringComparison.Ordinal)))
+        {
+            endpoint.Deliver(invalidation);
+        }
+    }
+
+    private sealed class Endpoint : IConfigurationInvalidationBus
+    {
+        private readonly FakeInvalidationBusFabric _fabric;
+        private readonly List<Action<ConfigurationInvalidation>> _handlers = new();
+
+        public Endpoint(FakeInvalidationBusFabric fabric, string originId)
+        {
+            _fabric = fabric;
+            OriginId = originId;
+        }
+
+        public string OriginId { get; }
+
+        public void Publish(ConfigurationInvalidationScope scope, string? target)
+            => _fabric.Broadcast(new ConfigurationInvalidation { Scope = scope, Target = target, OriginId = OriginId });
+
+        public void Subscribe(Action<ConfigurationInvalidation> handler)
+            => _handlers.Add(handler);
+
+        public void Deliver(ConfigurationInvalidation invalidation)
+        {
+            foreach (var handler in _handlers)
+            {
+                handler(invalidation);
+            }
+        }
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/LibraryVisibilityPropagationTests.cs

@@ -0,0 +1,161 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations.Configuration;
+using Emby.Server.Implementations.Serialization;
+using Jellyfin.Data;
+using Jellyfin.Database.Implementations.Entities;
+using Jellyfin.Database.Implementations.Enums;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Controller;
+using MediaBrowser.Controller.Entities;
+using MediaBrowser.Model.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using Moq;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// Library options are cached in a process-wide dictionary, so the replica that did not serve the admin's
+/// request is the one under test here: the other replica's write reaches the shared library directory, and
+/// this one has to stop answering out of its own stale copy.
+/// </summary>
+/// <remarks>
+/// Disabling a library is an access revocation that overrides every per-user check, so a stale replica
+/// keeps serving content that is supposed to be hidden from everyone.
+/// </remarks>
+public sealed class LibraryVisibilityPropagationTests : IDisposable
+{
+    private readonly string _libraryPath;
+    private readonly MyXmlSerializer _serializer = new MyXmlSerializer();
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="LibraryVisibilityPropagationTests"/> class.
+    /// </summary>
+    public LibraryVisibilityPropagationTests()
+    {
+        _libraryPath = Path.Combine(Path.GetTempPath(), "jf-library-prop-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(_libraryPath);
+
+        var applicationHost = new Mock<IServerApplicationHost>();
+        applicationHost.Setup(host => host.ExpandVirtualPath(It.IsAny<string>())).Returns<string>(path => path);
+        applicationHost.Setup(host => host.ReverseVirtualPath(It.IsAny<string>())).Returns<string>(path => path);
+
+        CollectionFolder.XmlSerializer = _serializer;
+        CollectionFolder.ApplicationHost = applicationHost.Object;
+    }
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        CollectionFolder.InvalidationBus = NullConfigurationInvalidationBus.Instance;
+        CollectionFolder.InvalidateAllLibraryOptions();
+
+        try
+        {
+            Directory.Delete(_libraryPath, true);
+        }
+        catch (IOException)
+        {
+        }
+    }
+
+    /// <summary>
+    /// Disabling a library on one replica has to hide it on every replica. Until it does, the ones that did
+    /// not serve the request keep the library visible to every user.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task LibraryDisabledOnAnotherInstance_IsNotVisibleHere()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var otherInstance = fabric.Connect("pod-a");
+        await SubscribeThisInstanceAsync(fabric);
+
+        WriteSharedOptions(enabled: true);
+
+        var user = CreateUser();
+        var library = new CollectionFolder { Path = _libraryPath, Name = "Movies" };
+
+        // This replica answers out of its cache from here on.
+        Assert.True(library.IsVisible(user));
+
+        // The admin disables the library on the other replica: it writes the shared directory and says so.
+        WriteSharedOptions(enabled: false);
+        otherInstance.Publish(ConfigurationInvalidationScope.LibraryOptions, _libraryPath);
+
+        Assert.False(library.IsVisible(user));
+        Assert.False(CollectionFolder.GetLibraryOptions(_libraryPath).Enabled);
+    }
+
+    /// <summary>
+    /// A path remap made on another replica has to reach this one, or it keeps resolving media against a
+    /// path that is no longer the library's.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task LibraryPathRemappedOnAnotherInstance_IsSeenHere()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var otherInstance = fabric.Connect("pod-a");
+        await SubscribeThisInstanceAsync(fabric);
+
+        WriteSharedOptions(enabled: true, mediaPath: "/media/old");
+        Assert.Equal("/media/old", CollectionFolder.GetLibraryOptions(_libraryPath).PathInfos[0].Path);
+
+        WriteSharedOptions(enabled: true, mediaPath: "/media/new");
+        otherInstance.Publish(ConfigurationInvalidationScope.LibraryOptions, _libraryPath);
+
+        Assert.Equal("/media/new", CollectionFolder.GetLibraryOptions(_libraryPath).PathInfos[0].Path);
+    }
+
+    /// <summary>
+    /// Saving library options here has to tell the other replicas, which is the half of the exchange the
+    /// tests above take as given.
+    /// </summary>
+    [Fact]
+    public void SaveLibraryOptions_AnnouncesTheLibraryToTheOtherInstances()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        ConfigurationInvalidation? received = null;
+
+        var otherInstance = fabric.Connect("pod-b");
+        otherInstance.Subscribe(invalidation => received = invalidation);
+        CollectionFolder.InvalidationBus = fabric.Connect("pod-a");
+
+        CollectionFolder.SaveLibraryOptions(_libraryPath, new LibraryOptions { Enabled = false });
+
+        Assert.NotNull(received);
+        Assert.Equal(ConfigurationInvalidationScope.LibraryOptions, received.Scope);
+        Assert.Equal(_libraryPath, received.Target);
+    }
+
+    private async Task SubscribeThisInstanceAsync(FakeInvalidationBusFabric fabric)
+    {
+        var bus = fabric.Connect("pod-b");
+        CollectionFolder.InvalidationBus = bus;
+
+        var subscriber = new ConfigurationInvalidationSubscriber(
+            bus,
+            Mock.Of<IConfigurationManager>(),
+            NullLogger<ConfigurationInvalidationSubscriber>.Instance);
+
+        await subscriber.StartAsync(CancellationToken.None);
+    }
+
+    private void WriteSharedOptions(bool enabled, string mediaPath = "/media")
+    {
+        // Written the way the other replica writes it, straight onto the shared directory.
+        var options = new LibraryOptions { Enabled = enabled, PathInfos = [new MediaPathInfo(mediaPath)] };
+        _serializer.SerializeToFile(options, Path.Combine(_libraryPath, "options.xml"));
+    }
+
+    private static User CreateUser()
+    {
+        var user = new User("propagation", "auth", "reset");
+        user.SetPermission(PermissionKind.EnableAllFolders, true);
+        return user;
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/RedisConfigurationInvalidationBusTests.cs

@@ -0,0 +1,104 @@
+using System;
+using System.Threading.Tasks;
+using Emby.Server.Implementations.Configuration;
+using MediaBrowser.Common.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using StackExchange.Redis;
+using Testcontainers.Redis;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// Round-trips <see cref="RedisConfigurationInvalidationBus"/> through a real Redis, the transport two
+/// replicas actually use to tell each other that the shared configuration directory has changed.
+/// </summary>
+[Trait("Category", "RequiresDocker")]
+public sealed class RedisConfigurationInvalidationBusTests : IAsyncLifetime
+{
+    private readonly RedisContainer _container;
+    private IConnectionMultiplexer? _redis;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RedisConfigurationInvalidationBusTests"/> class.
+    /// </summary>
+    public RedisConfigurationInvalidationBusTests()
+    {
+        _container = new RedisBuilder("redis:7-alpine").Build();
+    }
+
+    /// <inheritdoc />
+    public async ValueTask InitializeAsync()
+    {
+        await _container.StartAsync();
+        _redis = await ConnectionMultiplexer.ConnectAsync(_container.GetConnectionString());
+    }
+
+    /// <inheritdoc />
+    public async ValueTask DisposeAsync()
+    {
+        if (_redis is not null)
+        {
+            await _redis.DisposeAsync();
+        }
+
+        await _container.DisposeAsync();
+    }
+
+    /// <summary>
+    /// A notice published by one replica reaches the other, carrying enough to invalidate one entry.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Publish_ReachesTheOtherInstance()
+    {
+        var received = new TaskCompletionSource<ConfigurationInvalidation>();
+        var instanceA = CreateBus("pod-a");
+        var instanceB = CreateBus("pod-b");
+
+        instanceB.Subscribe(invalidation => received.TrySetResult(invalidation));
+
+        instanceA.Publish(ConfigurationInvalidationScope.LibraryOptions, "/media/movies");
+
+        var invalidation = await received.Task.WaitAsync(TimeSpan.FromSeconds(10), TestContext.Current.CancellationToken);
+        Assert.Equal(ConfigurationInvalidationScope.LibraryOptions, invalidation.Scope);
+        Assert.Equal("/media/movies", invalidation.Target);
+        Assert.Equal("pod-a", invalidation.OriginId);
+    }
+
+    /// <summary>
+    /// The publishing replica has already applied the change to its own cache, so it must not act on its
+    /// own notice and reload what it just wrote.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task Publish_IsNotDeliveredToThePublisher()
+    {
+        var ownNotice = new TaskCompletionSource<ConfigurationInvalidation>();
+        var otherNotice = new TaskCompletionSource<ConfigurationInvalidation>();
+        var instanceA = CreateBus("pod-a");
+        var instanceB = CreateBus("pod-b");
+
+        instanceA.Subscribe(invalidation => ownNotice.TrySetResult(invalidation));
+        instanceB.Subscribe(invalidation => otherNotice.TrySetResult(invalidation));
+
+        instanceA.Publish(ConfigurationInvalidationScope.SystemConfiguration, null);
+
+        // Ordering is per channel, so B having the notice means A would have had it too.
+        await otherNotice.Task.WaitAsync(TimeSpan.FromSeconds(10), TestContext.Current.CancellationToken);
+        Assert.False(ownNotice.Task.IsCompleted);
+    }
+
+    private RedisConfigurationInvalidationBus CreateBus(string originId)
+    {
+        Environment.SetEnvironmentVariable("JELLYFIN_INSTANCE_ID", originId);
+        try
+        {
+            return new RedisConfigurationInvalidationBus(_redis!, NullLogger<RedisConfigurationInvalidationBus>.Instance);
+        }
+        finally
+        {
+            Environment.SetEnvironmentVariable("JELLYFIN_INSTANCE_ID", null);
+        }
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/RemoteInvalidationApplyTests.cs

@@ -0,0 +1,205 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations;
+using Emby.Server.Implementations.Configuration;
+using Emby.Server.Implementations.Serialization;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Common.Net;
+using MediaBrowser.Controller.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// Applying an invalidation re-raises the same update events a local save raises, and some consumers of
+/// those events answer an update by writing - <c>RecordingsManager</c> creating the recording folders for
+/// the <c>livetv</c> key, <c>ApplicationHost</c> clearing <c>IsPortAuthorized</c> on a port change. The
+/// instance that did not write must not repeat those writes, and no write it is induced into must reach
+/// the bus.
+/// </summary>
+public sealed class RemoteInvalidationApplyTests : IDisposable
+{
+    private readonly string _root;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RemoteInvalidationApplyTests"/> class.
+    /// </summary>
+    public RemoteInvalidationApplyTests()
+    {
+        _root = Path.Combine(Path.GetTempPath(), "jf-config-apply-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(_root);
+    }
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        try
+        {
+            Directory.Delete(_root, true);
+        }
+        catch (IOException)
+        {
+        }
+    }
+
+    /// <summary>
+    /// A consumer that knows nothing about the bus - a plugin, or anything reached transitively from one -
+    /// can answer an applied invalidation by writing. That write must not become a notice of its own.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task NamedInvalidation_InducingAWriteOnTheReceiver_DoesNotPublishBack()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        var receivedByA = 0;
+        instanceA.InvalidationBus.Subscribe(_ => Interlocked.Increment(ref receivedByA));
+
+        var writesByB = 0;
+        instanceB.NamedConfigurationUpdated += (_, e) =>
+        {
+            // One shot: the induced write raises the event again on this instance.
+            if (Interlocked.Increment(ref writesByB) > 1)
+            {
+                return;
+            }
+
+            var configuration = (NetworkConfiguration)instanceB.GetConfiguration(e.Key);
+            configuration.PublishedServerUriBySubnet = ["10.0.0.0/8=example"];
+            instanceB.SaveConfiguration(e.Key, configuration);
+        };
+
+        var updated = instanceA.GetNetworkConfiguration();
+        updated.EnableRemoteAccess = false;
+        instanceA.SaveConfiguration(NetworkConfigurationStore.StoreKey, updated);
+
+        Assert.Equal(0, receivedByA);
+
+        // The point of the bus still holds: B is not left on its stale copy.
+        Assert.False(instanceB.GetNetworkConfiguration().EnableRemoteAccess);
+    }
+
+    /// <summary>
+    /// The shape of <c>RecordingsManager</c>: a consumer that answers a named configuration update by
+    /// writing has to be able to tell that the write was another instance's, and skip it.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task NamedInvalidation_WithAWriteTriggeringConsumer_DoesNotDuplicateTheWrite()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        var receivedByA = 0;
+        instanceA.InvalidationBus.Subscribe(_ => Interlocked.Increment(ref receivedByA));
+
+        var writesByB = 0;
+        instanceB.NamedConfigurationUpdated += (_, e) =>
+        {
+            if (ConfigurationInvalidationContext.IsApplyingRemoteInvalidation)
+            {
+                return;
+            }
+
+            Interlocked.Increment(ref writesByB);
+        };
+
+        var updated = instanceA.GetNetworkConfiguration();
+        updated.EnableRemoteAccess = false;
+        instanceA.SaveConfiguration(NetworkConfigurationStore.StoreKey, updated);
+
+        Assert.Equal(0, writesByB);
+        Assert.Equal(0, receivedByA);
+        Assert.False(instanceB.GetNetworkConfiguration().EnableRemoteAccess);
+
+        // A read-only consumer is still told, which is what the invalidation exists for.
+        var refreshes = 0;
+        instanceB.NamedConfigurationUpdated += (_, _) => Interlocked.Increment(ref refreshes);
+
+        updated.EnableRemoteAccess = true;
+        instanceA.SaveConfiguration(NetworkConfigurationStore.StoreKey, updated);
+
+        Assert.Equal(1, refreshes);
+    }
+
+    /// <summary>
+    /// The <c>ApplicationHost.IsPortAuthorized</c> class of consumer: the system configuration event is
+    /// queued rather than raised inline, so the fix has to survive the hop onto the thread pool.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task SystemInvalidation_InducingAQueuedWriteOnTheReceiver_DoesNotPublishBack()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        var receivedByA = 0;
+        instanceA.InvalidationBus.Subscribe(_ => Interlocked.Increment(ref receivedByA));
+
+        var applied = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+        var handled = 0;
+        instanceB.ConfigurationUpdated += (_, _) =>
+        {
+            if (Interlocked.Increment(ref handled) > 1)
+            {
+                return;
+            }
+
+            instanceB.Configuration.IsPortAuthorized = false;
+            instanceB.SaveConfiguration();
+            applied.TrySetResult();
+        };
+
+        instanceA.Configuration.QuickConnectAvailable = false;
+        instanceA.SaveConfiguration();
+
+        await applied.Task.WaitAsync(TimeSpan.FromSeconds(10), TestContext.Current.CancellationToken);
+
+        Assert.Equal(0, receivedByA);
+        Assert.False(instanceB.Configuration.QuickConnectAvailable);
+    }
+
+    private async Task<ServerConfigurationManager> CreateSubscribedInstanceAsync(FakeInvalidationBusFabric fabric, string originId)
+    {
+        var instance = CreateInstance(fabric, originId);
+        var subscriber = new ConfigurationInvalidationSubscriber(
+            instance.InvalidationBus,
+            instance,
+            NullLogger<ConfigurationInvalidationSubscriber>.Instance);
+
+        await subscriber.StartAsync(CancellationToken.None);
+        return instance;
+    }
+
+    private ServerConfigurationManager CreateInstance(FakeInvalidationBusFabric fabric, string originId)
+    {
+        var paths = new ServerApplicationPaths(
+            Ensure("data"),
+            Ensure("log"),
+            Ensure("config"),
+            Ensure("cache"),
+            Ensure("web"));
+
+        var manager = new ServerConfigurationManager(paths, NullLoggerFactory.Instance, new MyXmlSerializer())
+        {
+            InvalidationBus = fabric.Connect(originId)
+        };
+
+        manager.AddParts([new NetworkConfigurationFactory()]);
+        return manager;
+    }
+
+    private string Ensure(string name)
+    {
+        var path = Path.Combine(_root, name);
+        Directory.CreateDirectory(path);
+        return path;
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Configuration/SharedConfigurationPropagationTests.cs

@@ -0,0 +1,147 @@
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Emby.Server.Implementations;
+using Emby.Server.Implementations.Configuration;
+using Emby.Server.Implementations.Serialization;
+using MediaBrowser.Common.Configuration;
+using MediaBrowser.Common.Net;
+using MediaBrowser.Controller.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+using StackExchange.Redis;
+using Xunit;
+
+namespace Jellyfin.Server.Implementations.Tests.Configuration;
+
+/// <summary>
+/// Two independently constructed <see cref="ServerConfigurationManager"/> instances over one configuration
+/// directory are the in-process stand-in for two replicas sharing one <c>/config</c> mount: what either of
+/// them writes, the other has to pick up without being restarted.
+/// </summary>
+public sealed class SharedConfigurationPropagationTests : IDisposable
+{
+    private readonly string _root;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SharedConfigurationPropagationTests"/> class.
+    /// </summary>
+    public SharedConfigurationPropagationTests()
+    {
+        _root = Path.Combine(Path.GetTempPath(), "jf-config-prop-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(_root);
+    }
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        try
+        {
+            Directory.Delete(_root, true);
+        }
+        catch (IOException)
+        {
+        }
+    }
+
+    /// <summary>
+    /// A system configuration setting tightened on one replica has to hold on every other replica, not
+    /// only on the one that served the admin's request.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task SystemConfigurationSavedOnOneInstance_IsSeenByAnotherWithoutRestart()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        // B has the pre-change configuration in hand before A writes, as a running replica would.
+        Assert.True(instanceB.Configuration.QuickConnectAvailable);
+
+        instanceA.Configuration.QuickConnectAvailable = false;
+        instanceA.SaveConfiguration();
+
+        Assert.False(instanceB.Configuration.QuickConnectAvailable);
+    }
+
+    /// <summary>
+    /// The same has to hold for the named configurations, which are cached per key and never reloaded.
+    /// </summary>
+    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
+    [Fact]
+    public async Task NamedConfigurationSavedOnOneInstance_IsSeenByAnotherWithoutRestart()
+    {
+        var fabric = new FakeInvalidationBusFabric();
+        var instanceA = CreateInstance(fabric, "pod-a");
+        var instanceB = await CreateSubscribedInstanceAsync(fabric, "pod-b");
+
+        Assert.True(instanceB.GetNetworkConfiguration().EnableRemoteAccess);
+
+        var updated = instanceA.GetNetworkConfiguration();
+        updated.EnableRemoteAccess = false;
+        instanceA.SaveConfiguration(NetworkConfigurationStore.StoreKey, updated);
+
+        Assert.False(instanceB.GetNetworkConfiguration().EnableRemoteAccess);
+    }
+
+    /// <summary>
+    /// A replica that cannot reach the bus keeps serving: the admin's save still lands on the shared
+    /// directory, and the only loss is that the other replicas are not told about it.
+    /// </summary>
+    [Fact]
+    public void SaveConfiguration_WithUnreachableBus_DoesNotThrow()
+    {
+        using var multiplexer = ConnectionMultiplexer.Connect("127.0.0.1:1,abortConnect=false,connectTimeout=200,connectRetry=1,syncTimeout=200");
+        var bus = new RedisConfigurationInvalidationBus(multiplexer, NullLogger<RedisConfigurationInvalidationBus>.Instance);
+
+        bus.Subscribe(_ => throw new InvalidOperationException("Nothing can be delivered by an unreachable bus."));
+
+        var instance = CreateInstance(new FakeInvalidationBusFabric(), "pod-a");
+        instance.InvalidationBus = bus;
+
+        instance.Configuration.QuickConnectAvailable = false;
+        instance.SaveConfiguration();
+        instance.SaveConfiguration(NetworkConfigurationStore.StoreKey, instance.GetNetworkConfiguration());
+
+        Assert.False(instance.Configuration.QuickConnectAvailable);
+    }
+
+    private async Task<ServerConfigurationManager> CreateSubscribedInstanceAsync(FakeInvalidationBusFabric fabric, string originId)
+    {
+        var instance = CreateInstance(fabric, originId);
+        var subscriber = new ConfigurationInvalidationSubscriber(
+            instance.InvalidationBus,
+            instance,
+            NullLogger<ConfigurationInvalidationSubscriber>.Instance);
+
+        await subscriber.StartAsync(CancellationToken.None);
+        return instance;
+    }
+
+    private ServerConfigurationManager CreateInstance(FakeInvalidationBusFabric fabric, string originId)
+    {
+        // Every instance has its own paths object, all of them pointing at the one shared directory.
+        var paths = new ServerApplicationPaths(
+            Ensure("data"),
+            Ensure("log"),
+            Ensure("config"),
+            Ensure("cache"),
+            Ensure("web"));
+
+        var manager = new ServerConfigurationManager(paths, NullLoggerFactory.Instance, new MyXmlSerializer())
+        {
+            InvalidationBus = fabric.Connect(originId)
+        };
+
+        manager.AddParts([new NetworkConfigurationFactory()]);
+        return manager;
+    }
+
+    private string Ensure(string name)
+    {
+        var path = Path.Combine(_root, name);
+        Directory.CreateDirectory(path);
+        return path;
+    }
+}

tests/Jellyfin.Server.Implementations.Tests/Library/LibraryManagerSortTests.cs

@@ -7,7 +7,6 @@ using Emby.Naming.Common;
 using Emby.Server.Implementations.Library;
 using Emby.Server.Implementations.Sorting;
 using Jellyfin.Data.Enums;
-using Jellyfin.Database.Implementations.Entities;
 using Jellyfin.Database.Implementations.Enums;
 using MediaBrowser.Controller.Configuration;
 using MediaBrowser.Controller.Entities;
@@ -64,49 +63,13 @@ public class LibraryManagerSortTests
         Assert.Equal(new[] { "Alpha", "Mike", "Zulu" }, sorted.Select(i => i.Name));
     }
 
-    [Fact]
-    public void Sort_ComparerThatIgnoresPrefetchedUserData_StillSortsFromLiveReads()
-    {
-        var alpha = new Audio { Name = "Alpha", SortName = "Alpha", Id = Guid.NewGuid() };
-        var zulu = new Audio { Name = "Zulu", SortName = "Zulu", Id = Guid.NewGuid() };
-        var playCounts = new Dictionary<Guid, int> { [alpha.Id] = 1, [zulu.Id] = 9 };
-
-        var userDataManager = new Mock<IUserDataManager>();
-        userDataManager
-            .Setup(u => u.GetUserData(It.IsAny<User>(), It.IsAny<BaseItem>()))
-            .Returns<User, BaseItem>((_, item) => new UserItemData { Key = item.Id.ToString("N"), PlayCount = playCounts[item.Id] });
-        userDataManager
-            .Setup(u => u.GetUserDataBatch(It.IsAny<IReadOnlyList<BaseItem>>(), It.IsAny<User>()))
-            .Returns(new Dictionary<Guid, UserItemData>());
-
-        var libraryManager = CreateLibraryManager(
-            new IBaseItemComparer[] { new PluginPlayCountComparer() },
-            userDataManager);
-
-        var sorted = libraryManager.Sort(
-            new BaseItem[] { alpha, zulu },
-            new User("sorter", "provider", "provider"),
-            new[] { (ItemSortBy.PlayCount, SortOrder.Descending) }).ToArray();
-
-        Assert.Equal(new[] { "Zulu", "Alpha" }, sorted.Select(i => i.Name));
-        userDataManager.Verify(u => u.GetUserData(It.IsAny<User>(), It.IsAny<BaseItem>()), Times.AtLeastOnce);
-    }
-
     private static Folder MakeFolder(string name, DateTime dateLastMediaAdded)
         => new() { Name = name, Id = Guid.NewGuid(), DateLastMediaAdded = dateLastMediaAdded };
 
-    private static Emby.Server.Implementations.Library.LibraryManager CreateLibraryManager(
-        IReadOnlyCollection<IBaseItemComparer> comparers,
-        Mock<IUserDataManager>? userDataManager = null)
+    private static Emby.Server.Implementations.Library.LibraryManager CreateLibraryManager(IReadOnlyCollection<IBaseItemComparer> comparers)
     {
         var fixture = new Fixture().Customize(new AutoMoqCustomization());
         fixture.Register(() => new NamingOptions());
-
-        if (userDataManager is not null)
-        {
-            fixture.Inject(userDataManager.Object);
-        }
-
         var configMock = fixture.Freeze<Mock<IServerConfigurationManager>>();
         configMock.Setup(c => c.ApplicationPaths.ProgramDataPath).Returns("/data");
         BaseItem.ConfigurationManager ??= configMock.Object;
@@ -123,22 +86,4 @@ public class LibraryManagerSortTests
                 fixture.Create<IEnumerable<ILibraryPostScanTask>>()))
             .Create();
     }
-
-    /// <summary>
-    /// A comparer of the shape a third-party plugin ships: it implements
-    /// <see cref="IUserBaseItemComparer"/> without ever mentioning PrefetchedUserData.
-    /// </summary>
-    public sealed class PluginPlayCountComparer : IUserBaseItemComparer
-    {
-        public User User { get; set; } = null!;
-
-        public IUserManager UserManager { get; set; } = null!;
-
-        public IUserDataManager UserDataManager { get; set; } = null!;
-
-        public ItemSortBy Type => ItemSortBy.PlayCount;
-
-        public int Compare(BaseItem? x, BaseItem? y)
-            => UserDataManager.GetUserData(User, x!)!.PlayCount.CompareTo(UserDataManager.GetUserData(User, y!)!.PlayCount);
-    }
 }

tests/Jellyfin.Server.Implementations.Tests/Library/UserDataManagerTests.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Emby.Server.Implementations.Library;
 using Jellyfin.Database.Implementations;
 using Jellyfin.Database.Implementations.Entities;
@@ -48,12 +49,6 @@ public sealed class UserDataManagerTests : IDisposable
         {
             Id = Guid.NewGuid()
         };
-
-        using (var ctx = CreateDbContext())
-        {
-            ctx.Users.Add(_user);
-            ctx.SaveChanges();
-        }
     }
 
     public void Dispose()
@@ -83,23 +78,6 @@ public sealed class UserDataManagerTests : IDisposable
         };
     }
 
-    private void Seed(AudioBook item, params UserData[] rows)
-    {
-        using var ctx = CreateDbContext();
-        ctx.BaseItems.Add(new BaseItemEntity { Id = item.Id, Type = typeof(AudioBook).FullName! });
-        ctx.UserData.AddRange(rows);
-        ctx.SaveChanges();
-    }
-
-    private User CreateOtherUser()
-    {
-        var user = new User("other", "auth-provider", "reset-provider") { Id = Guid.NewGuid() };
-        using var ctx = CreateDbContext();
-        ctx.Users.Add(user);
-        ctx.SaveChanges();
-        return user;
-    }
-
     private UserData CreateUserDataRow(AudioBook item, string key, long positionTicks)
     {
         return new UserData
@@ -120,10 +98,11 @@ public sealed class UserDataManagerTests : IDisposable
         var currentKey = item.GetUserDataKeys()[0];
 
         // the retired-key row comes first to ensure selection is by key, not row order
-        Seed(
-            item,
+        item.UserData = new List<UserData>
+        {
             CreateUserDataRow(item, "Author-Old Album-0001Old File Name", 111),
-            CreateUserDataRow(item, currentKey, 222));
+            CreateUserDataRow(item, currentKey, 222)
+        };
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -138,10 +117,11 @@ public sealed class UserDataManagerTests : IDisposable
         var item = CreateAudioBook();
         var idKey = item.GetUserDataKeys()[1];
 
-        Seed(
-            item,
+        item.UserData = new List<UserData>
+        {
             CreateUserDataRow(item, "Author-Old Album-0001Old File Name", 111),
-            CreateUserDataRow(item, idKey, 333));
+            CreateUserDataRow(item, idKey, 333)
+        };
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -155,7 +135,10 @@ public sealed class UserDataManagerTests : IDisposable
     {
         var item = CreateAudioBook();
 
-        Seed(item, CreateUserDataRow(item, "Author-Old Album-0001Old File Name", 111));
+        item.UserData = new List<UserData>
+        {
+            CreateUserDataRow(item, "Author-Old Album-0001Old File Name", 111)
+        };
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -167,7 +150,7 @@ public sealed class UserDataManagerTests : IDisposable
     public void GetUserData_NoRows_ReturnsDefaultWithPrimaryKey()
     {
         var item = CreateAudioBook();
-        Seed(item);
+        item.UserData = new List<UserData>();
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -183,9 +166,13 @@ public sealed class UserDataManagerTests : IDisposable
         var currentKey = item.GetUserDataKeys()[0];
 
         var otherUserRow = CreateUserDataRow(item, currentKey, 999);
-        otherUserRow.UserId = CreateOtherUser().Id;
+        otherUserRow.UserId = Guid.NewGuid();
 
-        Seed(item, otherUserRow, CreateUserDataRow(item, currentKey, 222));
+        item.UserData = new List<UserData>
+        {
+            otherUserRow,
+            CreateUserDataRow(item, currentKey, 222)
+        };
 
         var userData = _userDataManager.GetUserData(_user, item);
 
@@ -196,15 +183,23 @@ public sealed class UserDataManagerTests : IDisposable
     [Fact]
     public void GetUserDataBatch_DatabaseFallback_ResolvesRowsByKeyOrder()
     {
+        // no preloaded navigation data, so the batch takes the database fallback
         var fossilItem = CreateAudioBook();
         var retiredItem = CreateAudioBook();
 
-        // the stale id-key row is inserted first so selection by row order would return it
-        Seed(
-            fossilItem,
-            CreateUserDataRow(fossilItem, fossilItem.GetUserDataKeys()[1], 111),
-            CreateUserDataRow(fossilItem, fossilItem.GetUserDataKeys()[0], 222));
-        Seed(retiredItem, CreateUserDataRow(retiredItem, "Author-Old Album-0001Old File Name", 333));
+        using (var ctx = CreateDbContext())
+        {
+            ctx.Users.Add(_user);
+            ctx.BaseItems.Add(new BaseItemEntity { Id = fossilItem.Id, Type = typeof(AudioBook).FullName! });
+            ctx.BaseItems.Add(new BaseItemEntity { Id = retiredItem.Id, Type = typeof(AudioBook).FullName! });
+
+            // the stale id-key row is inserted first so selection by row order would return it
+            ctx.UserData.AddRange(
+                CreateUserDataRow(fossilItem, fossilItem.GetUserDataKeys()[1], 111),
+                CreateUserDataRow(fossilItem, fossilItem.GetUserDataKeys()[0], 222),
+                CreateUserDataRow(retiredItem, "Author-Old Album-0001Old File Name", 333));
+            ctx.SaveChanges();
+        }
 
         var result = _userDataManager.GetUserDataBatch([fossilItem, retiredItem], _user);
 

tests/Jellyfin.Server.Implementations.Tests/TV/TVSeriesManagerNextUpTests.cs

@@ -1,94 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Globalization;
-using System.Linq;
-using Emby.Server.Implementations.TV;
-using Jellyfin.Database.Implementations.Entities;
-using MediaBrowser.Controller.Configuration;
-using MediaBrowser.Controller.Dto;
-using MediaBrowser.Controller.Entities;
-using MediaBrowser.Controller.Entities.TV;
-using MediaBrowser.Controller.Library;
-using MediaBrowser.Controller.Persistence;
-using MediaBrowser.Model.Configuration;
-using MediaBrowser.Model.Querying;
-using Moq;
-using Xunit;
-
-namespace Jellyfin.Server.Implementations.Tests.TV;
-
-public class TVSeriesManagerNextUpTests
-{
-    [Theory]
-    [InlineData(1)]
-    [InlineData(25)]
-    [InlineData(200)]
-    public void GetNextUp_ReadsUserDataInABoundedNumberOfQueries(int seriesCount)
-    {
-        var user = new User("next-up", "provider", "provider");
-        var libraryManager = new Mock<ILibraryManager>();
-        var userDataManager = new Mock<IUserDataManager>();
-
-        var seriesKeys = Enumerable.Range(0, seriesCount)
-            .Select(i => i.ToString(CultureInfo.InvariantCulture))
-            .ToList();
-
-        var batch = seriesKeys.ToDictionary(
-            key => key,
-            key => new NextUpEpisodeBatchResult
-            {
-                NextUp = new Episode { Id = Guid.NewGuid(), Name = "Next " + key },
-                LastWatched = new Episode { Id = Guid.NewGuid(), Name = "Watched " + key }
-            });
-
-        libraryManager
-            .Setup(l => l.GetNextUpSeriesKeys(It.IsAny<InternalItemsQuery>(), It.IsAny<IReadOnlyCollection<BaseItem>>(), It.IsAny<DateTime>()))
-            .Returns(seriesKeys);
-        libraryManager
-            .Setup(l => l.GetNextUpEpisodesBatch(It.IsAny<InternalItemsQuery>(), It.IsAny<IReadOnlyList<string>>(), It.IsAny<bool>(), It.IsAny<bool>()))
-            .Returns(batch);
-        libraryManager.Setup(l => l.GetLinkedAlternateVersions(It.IsAny<Video>())).Returns([]);
-        libraryManager.Setup(l => l.GetLocalAlternateVersionIds(It.IsAny<Video>())).Returns([]);
-
-        var batchReads = 0;
-        userDataManager
-            .Setup(u => u.GetUserDataBatch(It.IsAny<IReadOnlyList<BaseItem>>(), It.IsAny<User>()))
-            .Returns<IReadOnlyList<BaseItem>, User>((items, _) =>
-            {
-                batchReads++;
-                return items.DistinctBy(i => i.Id).ToDictionary(
-                    i => i.Id,
-                    i => new UserItemData { Key = i.Id.ToString("N", CultureInfo.InvariantCulture) });
-            });
-
-        var previousLibraryManager = BaseItem.LibraryManager;
-        BaseItem.LibraryManager = libraryManager.Object;
-
-        try
-        {
-            var manager = new TVSeriesManager(userDataManager.Object, libraryManager.Object, CreateConfigurationManager());
-
-            var result = manager.GetNextUp(
-                new NextUpQuery { User = user, EnableTotalRecordCount = true },
-                [],
-                new DtoOptions(false));
-
-            Assert.Equal(seriesCount, result.TotalRecordCount);
-
-            // Selection, the resume check and the last played date: three reads whatever the library holds.
-            Assert.Equal(3, batchReads);
-            userDataManager.Verify(u => u.GetUserData(It.IsAny<User>(), It.IsAny<BaseItem>()), Times.Never);
-        }
-        finally
-        {
-            BaseItem.LibraryManager = previousLibraryManager;
-        }
-    }
-
-    private static IServerConfigurationManager CreateConfigurationManager()
-    {
-        var configurationManager = new Mock<IServerConfigurationManager>();
-        configurationManager.SetupGet(c => c.Configuration).Returns(new ServerConfiguration());
-        return configurationManager.Object;
-    }
-}

tests/Jellyfin.Server.Tests/Library/UserDataManagerReplicaTests.cs

@@ -1,243 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Globalization;
-using System.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-using Emby.Server.Implementations.Library;
-using Jellyfin.Database.Implementations;
-using Jellyfin.Database.Implementations.DbConfiguration;
-using Jellyfin.Database.Implementations.Entities;
-using Jellyfin.Database.Implementations.Locking;
-using Jellyfin.Database.Providers.PostgreSQL;
-using Jellyfin.Server.Tests.Migrations;
-using MediaBrowser.Controller.Configuration;
-using MediaBrowser.Model.Configuration;
-using MediaBrowser.Model.Entities;
-using Microsoft.EntityFrameworkCore;
-using Microsoft.Extensions.Logging.Abstractions;
-using Moq;
-using Npgsql;
-using Xunit;
-using AudioBook = MediaBrowser.Controller.Entities.AudioBook;
-
-namespace Jellyfin.Server.Tests.Library;
-
-/// <summary>
-/// Two independently constructed <see cref="UserDataManager"/> instances over one PostgreSQL database are the
-/// in-process stand-in for two replicas sharing one database: what either of them writes, the other has to
-/// see on its very next read, and a read-modify-write on one must not roll back the other's.
-/// </summary>
-[Trait("Category", "RequiresDocker")]
-public sealed class UserDataManagerReplicaTests : IClassFixture<UserDataManagerReplicaTests.DatabaseFixture>
-{
-    private static readonly long _quarterIn = TimeSpan.FromMinutes(20).Ticks;
-
-    private readonly NpgsqlDataSource _dataSource;
-
-    public UserDataManagerReplicaTests(DatabaseFixture fixture)
-    {
-        _dataSource = fixture.DataSource;
-    }
-
-    /// <summary>
-    /// A resume position written by the replica serving the playback tick has to be the position the next
-    /// request reads, whichever replica it lands on - both through the single item read the write path uses
-    /// and through the batch read the library pages render from.
-    /// </summary>
-    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
-    [Fact]
-    public async Task ResumePositionWrittenOnOneReplica_IsReadOnAnother()
-    {
-        var cancellationToken = TestContext.Current.CancellationToken;
-        var itemId = Guid.NewGuid();
-        var user = await CreateUserAndItemAsync(_dataSource, itemId, cancellationToken);
-
-        var replicaA = CreateManager(_dataSource);
-        var replicaB = CreateManager(_dataSource);
-        var itemOnA = new AudioBook { Id = itemId, Name = "Replica Book" };
-        var itemOnB = new AudioBook { Id = itemId, Name = "Replica Book" };
-
-        var early = replicaA.GetUserData(user, itemOnA)!;
-        early.PlaybackPositionTicks = TimeSpan.FromMinutes(5).Ticks;
-        replicaA.SaveUserData(user, itemOnA, early, UserDataSaveReason.PlaybackProgress, cancellationToken);
-
-        // Replica B materialised the item before the later tick, so it holds the earlier row in memory.
-        itemOnB.UserData = await LoadUserDataAsync(_dataSource, itemId, cancellationToken);
-
-        var later = replicaA.GetUserData(user, itemOnA)!;
-        later.PlaybackPositionTicks = _quarterIn;
-        replicaA.SaveUserData(user, itemOnA, later, UserDataSaveReason.PlaybackProgress, cancellationToken);
-
-        Assert.Equal(_quarterIn, replicaB.GetUserData(user, itemOnB)!.PlaybackPositionTicks);
-        Assert.Equal(_quarterIn, replicaB.GetUserDataBatch([itemOnB], user)[itemId].PlaybackPositionTicks);
-    }
-
-    /// <summary>
-    /// The playback tick is a read-modify-write of the whole row, so a tick served by one replica must build
-    /// on the favourite another replica just recorded instead of writing it back out.
-    /// </summary>
-    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
-    [Fact]
-    public async Task PlaybackTickOnOneReplica_KeepsFavouriteSetOnAnother()
-    {
-        var cancellationToken = TestContext.Current.CancellationToken;
-        var itemId = Guid.NewGuid();
-        var user = await CreateUserAndItemAsync(_dataSource, itemId, cancellationToken);
-
-        var replicaA = CreateManager(_dataSource);
-        var replicaB = CreateManager(_dataSource);
-        var itemOnA = new AudioBook { Id = itemId, Name = "Replica Book" };
-        var itemOnB = new AudioBook { Id = itemId, Name = "Replica Book" };
-
-        var seed = replicaA.GetUserData(user, itemOnA)!;
-        seed.PlaybackPositionTicks = TimeSpan.FromMinutes(5).Ticks;
-        replicaA.SaveUserData(user, itemOnA, seed, UserDataSaveReason.PlaybackProgress, cancellationToken);
-
-        // Replica B is serving the playback session and read the item before the favourite was recorded.
-        itemOnB.UserData = await LoadUserDataAsync(_dataSource, itemId, cancellationToken);
-
-        var favourited = replicaA.GetUserData(user, itemOnA)!;
-        favourited.IsFavorite = true;
-        replicaA.SaveUserData(user, itemOnA, favourited, UserDataSaveReason.UpdateUserRating, cancellationToken);
-
-        var tick = replicaB.GetUserData(user, itemOnB)!;
-        tick.PlaybackPositionTicks = _quarterIn;
-        replicaB.SaveUserData(user, itemOnB, tick, UserDataSaveReason.PlaybackProgress, cancellationToken);
-
-        var stored = replicaA.GetUserData(user, itemOnA)!;
-        Assert.True(stored.IsFavorite);
-        Assert.Equal(_quarterIn, stored.PlaybackPositionTicks);
-    }
-
-    /// <summary>
-    /// A tick that lands on the other replica has to carry the position forward from where the session
-    /// actually is, not from the position that replica happened to have in memory.
-    /// </summary>
-    /// <returns>A <see cref="Task"/> representing the asynchronous operation.</returns>
-    [Fact]
-    public async Task PlaybackTickOnOneReplica_ResumesFromThePositionAnotherWrote()
-    {
-        var cancellationToken = TestContext.Current.CancellationToken;
-        var itemId = Guid.NewGuid();
-        var user = await CreateUserAndItemAsync(_dataSource, itemId, cancellationToken);
-
-        var replicaA = CreateManager(_dataSource);
-        var replicaB = CreateManager(_dataSource);
-        var itemOnA = new AudioBook { Id = itemId, Name = "Replica Book" };
-        var itemOnB = new AudioBook { Id = itemId, Name = "Replica Book" };
-
-        var seed = replicaA.GetUserData(user, itemOnA)!;
-        seed.PlaybackPositionTicks = TimeSpan.FromMinutes(5).Ticks;
-        replicaA.SaveUserData(user, itemOnA, seed, UserDataSaveReason.PlaybackProgress, cancellationToken);
-
-        itemOnB.UserData = await LoadUserDataAsync(_dataSource, itemId, cancellationToken);
-
-        // The viewer seeks forward and the tick reporting it lands on replica A.
-        var seeked = replicaA.GetUserData(user, itemOnA)!;
-        seeked.PlaybackPositionTicks = _quarterIn;
-        replicaA.SaveUserData(user, itemOnA, seeked, UserDataSaveReason.PlaybackProgress, cancellationToken);
-
-        // The next tick lands on replica B, which adds ten seconds to whatever it reads.
-        var tick = replicaB.GetUserData(user, itemOnB)!;
-        tick.PlaybackPositionTicks += TimeSpan.FromSeconds(10).Ticks;
-        replicaB.SaveUserData(user, itemOnB, tick, UserDataSaveReason.PlaybackProgress, cancellationToken);
-
-        var stored = replicaA.GetUserData(user, itemOnA)!;
-        Assert.Equal(_quarterIn + TimeSpan.FromSeconds(10).Ticks, stored.PlaybackPositionTicks);
-    }
-
-    private static UserDataManager CreateManager(NpgsqlDataSource dataSource)
-    {
-        var config = new Mock<IServerConfigurationManager>();
-        config.SetupGet(c => c.Configuration).Returns(new ServerConfiguration());
-        return new UserDataManager(config.Object, new DataSourceContextFactory(dataSource));
-    }
-
-    private static async Task<ICollection<UserData>> LoadUserDataAsync(NpgsqlDataSource dataSource, Guid itemId, CancellationToken cancellationToken)
-    {
-        var context = CreateContext(dataSource);
-        await using (context.ConfigureAwait(false))
-        {
-            return await context.UserData
-                .AsNoTracking()
-                .Where(e => e.ItemId.Equals(itemId))
-                .ToArrayAsync(cancellationToken)
-                .ConfigureAwait(false);
-        }
-    }
-
-    private static async Task<User> CreateUserAndItemAsync(NpgsqlDataSource dataSource, Guid itemId, CancellationToken cancellationToken)
-    {
-        var context = CreateContext(dataSource);
-        await using (context.ConfigureAwait(false))
-        {
-            var user = new User("replica-user-" + itemId.ToString("N", CultureInfo.InvariantCulture), "provider", "provider");
-            context.Users.Add(user);
-            context.BaseItems.Add(new BaseItemEntity { Id = itemId, Type = typeof(AudioBook).FullName! });
-            await context.SaveChangesAsync(cancellationToken).ConfigureAwait(false);
-
-            return user;
-        }
-    }
-
-    private static JellyfinDbContext CreateContext(NpgsqlDataSource dataSource)
-    {
-        var optionsBuilder = new DbContextOptionsBuilder<JellyfinDbContext>();
-        var provider = new PostgreSqlDatabaseProvider(dataSource);
-        provider.Initialise(optionsBuilder, new DatabaseConfigurationOptions { DatabaseType = "PostgreSQL" });
-        return new JellyfinDbContext(
-            optionsBuilder.Options,
-            NullLogger<JellyfinDbContext>.Instance,
-            provider,
-            new NoLockBehavior(NullLogger<NoLockBehavior>.Instance));
-    }
-
-    /// <summary>
-    /// Hands every <see cref="UserDataManager"/> its own context over the one shared database, the way the
-    /// pooled factory does in the server.
-    /// </summary>
-    private sealed class DataSourceContextFactory : IDbContextFactory<JellyfinDbContext>
-    {
-        private readonly NpgsqlDataSource _dataSource;
-
-        public DataSourceContextFactory(NpgsqlDataSource dataSource)
-        {
-            _dataSource = dataSource;
-        }
-
-        public JellyfinDbContext CreateDbContext() => CreateContext(_dataSource);
-    }
-
-    /// <summary>
-    /// Builds the schema once for the whole class. Every test keeps to its own user and item, so one
-    /// database serves all of them and the shared server is spared three schema builds.
-    /// </summary>
-    public sealed class DatabaseFixture : IAsyncLifetime
-    {
-        private PostgreSqlTestServer _server = null!;
-
-        public NpgsqlDataSource DataSource { get; private set; } = null!;
-
-        /// <inheritdoc/>
-        public async ValueTask InitializeAsync()
-        {
-            _server = await PostgreSqlTestServer.StartAsync().ConfigureAwait(false);
-            var connectionString = await _server.CreateDatabaseAsync("userdata_replica", CancellationToken.None).ConfigureAwait(false);
-            DataSource = new NpgsqlDataSourceBuilder(connectionString).Build();
-
-            var context = CreateContext(DataSource);
-            await using (context.ConfigureAwait(false))
-            {
-                await context.Database.EnsureCreatedAsync(CancellationToken.None).ConfigureAwait(false);
-            }
-        }
-
-        /// <inheritdoc/>
-        public async ValueTask DisposeAsync()
-        {
-            await DataSource.DisposeAsync().ConfigureAwait(false);
-            await _server.DisposeAsync().ConfigureAwait(false);
-        }
-    }
-}