Performance improvements:

1. Caching for app tags
2. Caching for available languages.

src/Squidex.Domain.Apps.Core.Operations/Tags/ITagService.cs

@@ -19,11 +19,11 @@ namespace Squidex.Domain.Apps.Core.Tags
 
         Task<Dictionary<string, string>> DenormalizeTagsAsync(Guid appId, string group, HashSet<string> ids);
 
-        Task<Dictionary<string, int>> GetTagsAsync(Guid appId, string group);
+        Task<TagsSet> GetTagsAsync(Guid appId, string group);
 
-        Task<TagSet> GetExportableTagsAsync(Guid appId, string group);
+        Task<TagsExport> GetExportableTagsAsync(Guid appId, string group);
 
-        Task RebuildTagsAsync(Guid appId, string group, TagSet tags);
+        Task RebuildTagsAsync(Guid appId, string group, TagsExport tags);
 
         Task ClearAsync(Guid appId, string group);
     }

src/Squidex.Domain.Apps.Core.Operations/Tags/TagSet.cs → src/Squidex.Domain.Apps.Core.Operations/Tags/TagsExport.cs

@@ -9,7 +9,7 @@ using System.Collections.Generic;
 
 namespace Squidex.Domain.Apps.Core.Tags
 {
-    public sealed class TagSet : Dictionary<string, Tag>
+    public sealed class TagsExport : Dictionary<string, Tag>
     {
     }
 }

src/Squidex.Domain.Apps.Core.Operations/Tags/TagsSet.cs

@@ -0,0 +1,26 @@
+// ==========================================================================
+//  Squidex Headless CMS
+// ==========================================================================
+//  Copyright (c) Squidex UG (haftungsbeschraenkt)
+//  All rights reserved. Licensed under the MIT license.
+// ==========================================================================
+
+using System.Collections.Generic;
+
+namespace Squidex.Domain.Apps.Core.Tags
+{
+    public sealed class TagsSet : Dictionary<string, int>
+    {
+        public long Version { get; set; }
+
+        public TagsSet()
+        {
+        }
+
+        public TagsSet(IDictionary<string, int> tags, long version)
+            : base(tags)
+        {
+            Version = version;
+        }
+    }
+}

src/Squidex.Domain.Apps.Entities/Assets/BackupAssets.cs

@@ -82,7 +82,7 @@ namespace Squidex.Domain.Apps.Entities.Assets
 
         private async Task RestoreTagsAsync(Guid appId, BackupReader reader)
         {
-            var tags = await reader.ReadJsonAttachmentAsync<TagSet>(TagsFile);
+            var tags = await reader.ReadJsonAttachmentAsync<TagsExport>(TagsFile);
 
             await tagService.RebuildTagsAsync(appId, TagGroups.Assets, tags);
         }

src/Squidex.Domain.Apps.Entities/Tags/GrainTagService.cs

@@ -45,17 +45,17 @@ namespace Squidex.Domain.Apps.Entities.Tags
             return GetGrain(appId, group).DenormalizeTagsAsync(ids);
         }
 
-        public Task<Dictionary<string, int>> GetTagsAsync(Guid appId, string group)
+        public Task<TagsSet> GetTagsAsync(Guid appId, string group)
         {
             return GetGrain(appId, group).GetTagsAsync();
         }
 
-        public Task<TagSet> GetExportableTagsAsync(Guid appId, string group)
+        public Task<TagsExport> GetExportableTagsAsync(Guid appId, string group)
         {
             return GetGrain(appId, group).GetExportableTagsAsync();
         }
 
-        public Task RebuildTagsAsync(Guid appId, string group, TagSet tags)
+        public Task RebuildTagsAsync(Guid appId, string group, TagsExport tags)
         {
             return GetGrain(appId, group).RebuildAsync(tags);
         }

src/Squidex.Domain.Apps.Entities/Tags/ITagGrain.cs

@@ -20,12 +20,12 @@ namespace Squidex.Domain.Apps.Entities.Tags
 
         Task<Dictionary<string, string>> DenormalizeTagsAsync(HashSet<string> ids);
 
-        Task<Dictionary<string, int>> GetTagsAsync();
+        Task<TagsSet> GetTagsAsync();
 
-        Task<TagSet> GetExportableTagsAsync();
+        Task<TagsExport> GetExportableTagsAsync();
 
         Task ClearAsync();
 
-        Task RebuildAsync(TagSet tags);
+        Task RebuildAsync(TagsExport tags);
     }
 }

src/Squidex.Domain.Apps.Entities/Tags/TagGrain.cs

@@ -20,7 +20,7 @@ namespace Squidex.Domain.Apps.Entities.Tags
         [CollectionName("Index_Tags")]
         public sealed class GrainState
         {
-            public TagSet Tags { get; set; } = new TagSet();
+            public TagsExport Tags { get; set; } = new TagsExport();
         }
 
         public TagGrain(IStore<string> store)
@@ -33,7 +33,7 @@ namespace Squidex.Domain.Apps.Entities.Tags
             return ClearStateAsync();
         }
 
-        public Task RebuildAsync(TagSet tags)
+        public Task RebuildAsync(TagsExport tags)
         {
             State.Tags = tags;
 
@@ -132,12 +132,14 @@ namespace Squidex.Domain.Apps.Entities.Tags
             return Task.FromResult(result);
         }
 
-        public Task<Dictionary<string, int>> GetTagsAsync()
+        public Task<TagsSet> GetTagsAsync()
         {
-            return Task.FromResult(State.Tags.Values.ToDictionary(x => x.Name, x => x.Count));
+            var tags = State.Tags.Values.ToDictionary(x => x.Name, x => x.Count);
+
+            return Task.FromResult(new TagsSet(tags, Persistence.Version));
         }
 
-        public Task<TagSet> GetExportableTagsAsync()
+        public Task<TagsExport> GetExportableTagsAsync()
         {
             return Task.FromResult(State.Tags);
         }

src/Squidex/Areas/Api/Controllers/Assets/AssetsController.cs

@@ -77,9 +77,11 @@ namespace Squidex.Areas.Api.Controllers.Assets
         [ApiCosts(1)]
         public async Task<IActionResult> GetTags(string app)
         {
-            var response = await tagService.GetTagsAsync(AppId, TagGroups.Assets);
+            var tags = await tagService.GetTagsAsync(AppId, TagGroups.Assets);
 
-            return Ok(response);
+            Response.Headers[HeaderNames.ETag] = tags.Version.ToString();
+
+            return Ok(tags);
         }
 
         /// <summary>

src/Squidex/app/shared/state/languages.state.ts

@@ -7,7 +7,7 @@
 
 import { Injectable } from '@angular/core';
 import { forkJoin, Observable } from 'rxjs';
-import { map, tap } from 'rxjs/operators';
+import { map, shareReplay, tap } from 'rxjs/operators';
 
 import {
     DialogService,
@@ -65,6 +65,8 @@ type LanguageResultList = ImmutableArray<SnapshotLanguage>;
 
 @Injectable()
 export class LanguagesState extends State<Snapshot> {
+    private cachedLanguage$: Observable<LanguageDto[]>;
+
     public languages =
         this.project(x => x.languages);
 
@@ -96,9 +98,7 @@ export class LanguagesState extends State<Snapshot> {
             this.resetState();
         }
 
-        return forkJoin(
-                this.languagesService.getLanguages(),
-                this.appLanguagesService.getLanguages(this.appName)).pipe(
+        return forkJoin(this.getAllLanguages(), this.getAppLanguages()).pipe(
             map(args => {
                 return { allLanguages: args[0], languages: args[1] };
             }),
@@ -166,6 +166,20 @@ export class LanguagesState extends State<Snapshot> {
         return this.snapshot.version;
     }
 
+    private getAppLanguages() {
+        return this.appLanguagesService.getLanguages(this.appName);
+    }
+
+    private getAllLanguages() {
+        if (!this.cachedLanguage$) {
+            this.cachedLanguage$ =
+                this.languagesService.getLanguages().pipe(
+                    shareReplay(1));
+        }
+
+        return this.cachedLanguage$;
+    }
+
     private createLanguage(language: AppLanguageDto, languages: AppLanguagesList): SnapshotLanguage {
         return {
             language,

tests/Squidex.Domain.Apps.Entities.Tests/Tags/GrainTagServiceTests.cs

@@ -48,7 +48,7 @@ namespace Squidex.Domain.Apps.Entities.Tags
         [Fact]
         public async Task Should_call_grain_when_rebuilding()
         {
-            var tags = new TagSet();
+            var tags = new TagsExport();
 
             await sut.RebuildTagsAsync(appId, TagGroups.Assets, tags);
 

tests/Squidex.Domain.Apps.Entities.Tests/Tags/TagGrainTests.cs

@@ -50,7 +50,7 @@ namespace Squidex.Domain.Apps.Entities.Tags
         [Fact]
         public async Task Should_rebuild_tags()
         {
-            var tags = new TagSet
+            var tags = new TagsExport
             {
                 ["id1"] = new Tag { Name = "name1", Count = 1 },
                 ["id2"] = new Tag { Name = "name2", Count = 2 },