Misskey® Reactions Buffering Technology™ (#14579)

* wip

* wip

* Update ReactionsBufferingService.ts

* Update ReactionsBufferingService.ts

* wip

* wip

* wip

* Update ReactionsBufferingService.ts

* wip

* wip

* wip

* Update NoteEntityService.ts

* wip

* wip

* wip

* wip

* Update CHANGELOG.md

29 files changed, 498 insertions, 92 deletions

diff --git a/.config/cypress-devcontainer.yml b/.config/cypress-devcontainer.yml
index e8da5f5e27..91dce35155 100644
--- a/.config/cypress-devcontainer.yml
+++ b/.config/cypress-devcontainer.yml
@@ -103,6 +103,14 @@ redis:
 #  #prefix: example-prefix
 #  #db: 1
 
+#redisForReactions:
+#  host: redis
+#  port: 6379
+#  #family: 0  # 0=Both, 4=IPv4, 6=IPv6
+#  #pass: example-pass
+#  #prefix: example-prefix
+#  #db: 1
+
 #   ┌───────────────────────────┐
 #───┘ MeiliSearch configuration └─────────────────────────────
 
diff --git a/.config/docker_example.yml b/.config/docker_example.yml
index d347882d1a..3f8e5734ce 100644
--- a/.config/docker_example.yml
+++ b/.config/docker_example.yml
@@ -106,6 +106,14 @@ redis:
 #  #prefix: example-prefix
 #  #db: 1
 
+#redisForReactions:
+#  host: redis
+#  port: 6379
+#  #family: 0  # 0=Both, 4=IPv4, 6=IPv6
+#  #pass: example-pass
+#  #prefix: example-prefix
+#  #db: 1
+
 #   ┌───────────────────────────┐
 #───┘ MeiliSearch configuration └─────────────────────────────
 
diff --git a/.config/example.yml b/.config/example.yml
index b11cbd1373..7080159117 100644
--- a/.config/example.yml
+++ b/.config/example.yml
@@ -172,6 +172,16 @@ redis:
 #  # You can specify more ioredis options...
 #  #username: example-username
 
+#redisForReactions:
+#  host: localhost
+#  port: 6379
+#  #family: 0  # 0=Both, 4=IPv4, 6=IPv6
+#  #pass: example-pass
+#  #prefix: example-prefix
+#  #db: 1
+#  # You can specify more ioredis options...
+#  #username: example-username
+
 #   ┌───────────────────────────┐
 #───┘ MeiliSearch configuration └─────────────────────────────
 
diff --git a/.devcontainer/devcontainer.yml b/.devcontainer/devcontainer.yml
index beefcfd0a2..3eb4fc2879 100644
--- a/.devcontainer/devcontainer.yml
+++ b/.devcontainer/devcontainer.yml
@@ -103,6 +103,14 @@ redis:
 #  #prefix: example-prefix
 #  #db: 1
 
+#redisForReactions:
+#  host: redis
+#  port: 6379
+#  #family: 0  # 0=Both, 4=IPv4, 6=IPv6
+#  #pass: example-pass
+#  #prefix: example-prefix
+#  #db: 1
+
 #   ┌───────────────────────────┐
 #───┘ MeiliSearch configuration └─────────────────────────────
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 65ed505c0e..a2d2e62a62 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@
 - Fix: 設定変更時のリロード確認ダイアログが複数個表示されることがある問題を修正
 
 ### Server
+- Feat: Misskey® Reactions Buffering Technology™ (RBT)により、リアクションの作成負荷を低減することが可能に
 - Fix: アンテナの書き込み時にキーワードが与えられなかった場合のエラーをApiErrorとして投げるように
   - この変更により、公式フロントエンドでは入力の不備が内部エラーとして報告される代わりに一般的なエラーダイアログで報告されます
 - Fix: ファイルがサイズの制限を超えてアップロードされた際にエラーを返さなかった問題を修正
diff --git a/chart/files/default.yml b/chart/files/default.yml
index f98b8ebfee..4d17131c25 100644
--- a/chart/files/default.yml
+++ b/chart/files/default.yml
@@ -124,6 +124,14 @@ redis:
 #  #prefix: example-prefix
 #  #db: 1
 
+#redisForReactions:
+#  host: redis
+#  port: 6379
+#  #family: 0  # 0=Both, 4=IPv4, 6=IPv6
+#  #pass: example-pass
+#  #prefix: example-prefix
+#  #db: 1
+
 #   ┌───────────────────────────┐
 #───┘ MeiliSearch configuration └─────────────────────────────
 
diff --git a/locales/index.d.ts b/locales/index.d.ts
index 339e625684..798cb89f83 100644
--- a/locales/index.d.ts
+++ b/locales/index.d.ts
@@ -5584,6 +5584,10 @@ export interface Locale extends ILocale {
          */
         "fanoutTimelineDbFallbackDescription": string;
         /**
+         * 有効にすると、リアクション作成時のパフォーマンスが大幅に向上し、データベースへの負荷を軽減することが可能です。ただし、Redisのメモリ使用量は増加します。
+         */
+        "reactionsBufferingDescription": string;
+        /**
          * 問い合わせ先URL
          */
         "inquiryUrl": string;
diff --git a/locales/ja-JP.yml b/locales/ja-JP.yml
index 2a5b530c9f..726e4f4ef4 100644
--- a/locales/ja-JP.yml
+++ b/locales/ja-JP.yml
@@ -1411,6 +1411,7 @@ _serverSettings:
   fanoutTimelineDescription: "有効にすると、各種タイムラインを取得する際のパフォーマンスが大幅に向上し、データベースへの負荷を軽減することが可能です。ただし、Redisのメモリ使用量は増加します。サーバーのメモリ容量が少ない場合、または動作が不安定な場合は無効にすることができます。"
   fanoutTimelineDbFallback: "データベースへのフォールバック"
   fanoutTimelineDbFallbackDescription: "有効にすると、タイムラインがキャッシュされていない場合にDBへ追加で問い合わせを行うフォールバック処理を行います。無効にすると、フォールバック処理を行わないことでさらにサーバーの負荷を軽減することができますが、タイムラインが取得できる範囲に制限が生じます。"
+  reactionsBufferingDescription: "有効にすると、リアクション作成時のパフォーマンスが大幅に向上し、データベースへの負荷を軽減することが可能です。ただし、Redisのメモリ使用量は増加します。"
   inquiryUrl: "問い合わせ先URL"
   inquiryUrlDescription: "サーバー運営者へのお問い合わせフォームのURLや、運営者の連絡先等が記載されたWebページのURLを指定します。"
 
diff --git a/packages/backend/migration/1726804538569-reactions-buffering.js b/packages/backend/migration/1726804538569-reactions-buffering.js
new file mode 100644
index 0000000000..bc19e9cc8a
--- /dev/null
+++ b/packages/backend/migration/1726804538569-reactions-buffering.js
@@ -0,0 +1,16 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export class ReactionsBuffering1726804538569 {
+    name = 'ReactionsBuffering1726804538569'
+
+    async up(queryRunner) {
+        await queryRunner.query(`ALTER TABLE "meta" ADD "enableReactionsBuffering" boolean NOT NULL DEFAULT false`);
+    }
+
+    async down(queryRunner) {
+        await queryRunner.query(`ALTER TABLE "meta" DROP COLUMN "enableReactionsBuffering"`);
+    }
+}
diff --git a/packages/backend/src/GlobalModule.ts b/packages/backend/src/GlobalModule.ts
index 09971e8ca0..2ecc1f4742 100644
--- a/packages/backend/src/GlobalModule.ts
+++ b/packages/backend/src/GlobalModule.ts
@@ -78,11 +78,19 @@ const $redisForTimelines: Provider = {
 	inject: [DI.config],
 };
 
+const $redisForReactions: Provider = {
+	provide: DI.redisForReactions,
+	useFactory: (config: Config) => {
+		return new Redis.Redis(config.redisForReactions);
+	},
+	inject: [DI.config],
+};
+
 @Global()
 @Module({
 	imports: [RepositoryModule],
-	providers: [$config, $db, $meilisearch, $redis, $redisForPub, $redisForSub, $redisForTimelines],
-	exports: [$config, $db, $meilisearch, $redis, $redisForPub, $redisForSub, $redisForTimelines, RepositoryModule],
+	providers: [$config, $db, $meilisearch, $redis, $redisForPub, $redisForSub, $redisForTimelines, $redisForReactions],
+	exports: [$config, $db, $meilisearch, $redis, $redisForPub, $redisForSub, $redisForTimelines, $redisForReactions, RepositoryModule],
 })
 export class GlobalModule implements OnApplicationShutdown {
 	constructor(
@@ -91,6 +99,7 @@ export class GlobalModule implements OnApplicationShutdown {
 		@Inject(DI.redisForPub) private redisForPub: Redis.Redis,
 		@Inject(DI.redisForSub) private redisForSub: Redis.Redis,
 		@Inject(DI.redisForTimelines) private redisForTimelines: Redis.Redis,
+		@Inject(DI.redisForReactions) private redisForReactions: Redis.Redis,
 	) { }
 
 	public async dispose(): Promise<void> {
@@ -103,6 +112,7 @@ export class GlobalModule implements OnApplicationShutdown {
 			this.redisForPub.disconnect(),
 			this.redisForSub.disconnect(),
 			this.redisForTimelines.disconnect(),
+			this.redisForReactions.disconnect(),
 		]);
 	}
 
diff --git a/packages/backend/src/config.ts b/packages/backend/src/config.ts
index cbd6d1c086..97ba79c574 100644
--- a/packages/backend/src/config.ts
+++ b/packages/backend/src/config.ts
@@ -49,6 +49,7 @@ type Source = {
 	redisForPubsub?: RedisOptionsSource;
 	redisForJobQueue?: RedisOptionsSource;
 	redisForTimelines?: RedisOptionsSource;
+	redisForReactions?: RedisOptionsSource;
 	meilisearch?: {
 		host: string;
 		port: string;
@@ -171,6 +172,7 @@ export type Config = {
 	redisForPubsub: RedisOptions & RedisOptionsSource;
 	redisForJobQueue: RedisOptions & RedisOptionsSource;
 	redisForTimelines: RedisOptions & RedisOptionsSource;
+	redisForReactions: RedisOptions & RedisOptionsSource;
 	sentryForBackend: { options: Partial<Sentry.NodeOptions>; enableNodeProfiling: boolean; } | undefined;
 	sentryForFrontend: { options: Partial<Sentry.NodeOptions> } | undefined;
 	perChannelMaxNoteCacheCount: number;
@@ -251,6 +253,7 @@ export function loadConfig(): Config {
 		redisForPubsub: config.redisForPubsub ? convertRedisOptions(config.redisForPubsub, host) : redis,
 		redisForJobQueue: config.redisForJobQueue ? convertRedisOptions(config.redisForJobQueue, host) : redis,
 		redisForTimelines: config.redisForTimelines ? convertRedisOptions(config.redisForTimelines, host) : redis,
+		redisForReactions: config.redisForReactions ? convertRedisOptions(config.redisForReactions, host) : redis,
 		sentryForBackend: config.sentryForBackend,
 		sentryForFrontend: config.sentryForFrontend,
 		id: config.id,
diff --git a/packages/backend/src/const.ts b/packages/backend/src/const.ts
index a238f4973a..e3a61861f4 100644
--- a/packages/backend/src/const.ts
+++ b/packages/backend/src/const.ts
@@ -8,6 +8,8 @@ export const MAX_NOTE_TEXT_LENGTH = 3000;
 export const USER_ONLINE_THRESHOLD = 1000 * 60 * 10; // 10min
 export const USER_ACTIVE_THRESHOLD = 1000 * 60 * 60 * 24 * 3; // 3days
 
+export const PER_NOTE_REACTION_USER_PAIR_CACHE_MAX = 16;
+
 //#region hard limits
 // If you change DB_* values, you must also change the DB schema.
 
diff --git a/packages/backend/src/core/CoreModule.ts b/packages/backend/src/core/CoreModule.ts
index 674241ac12..3b3c35f976 100644
--- a/packages/backend/src/core/CoreModule.ts
+++ b/packages/backend/src/core/CoreModule.ts
@@ -50,6 +50,7 @@ import { PollService } from './PollService.js';
 import { PushNotificationService } from './PushNotificationService.js';
 import { QueryService } from './QueryService.js';
 import { ReactionService } from './ReactionService.js';
+import { ReactionsBufferingService } from './ReactionsBufferingService.js';
 import { RelayService } from './RelayService.js';
 import { RoleService } from './RoleService.js';
 import { S3Service } from './S3Service.js';
@@ -193,6 +194,7 @@ const $ProxyAccountService: Provider = { provide: 'ProxyAccountService', useExis
 const $PushNotificationService: Provider = { provide: 'PushNotificationService', useExisting: PushNotificationService };
 const $QueryService: Provider = { provide: 'QueryService', useExisting: QueryService };
 const $ReactionService: Provider = { provide: 'ReactionService', useExisting: ReactionService };
+const $ReactionsBufferingService: Provider = { provide: 'ReactionsBufferingService', useExisting: ReactionsBufferingService };
 const $RelayService: Provider = { provide: 'RelayService', useExisting: RelayService };
 const $RoleService: Provider = { provide: 'RoleService', useExisting: RoleService };
 const $S3Service: Provider = { provide: 'S3Service', useExisting: S3Service };
@@ -342,6 +344,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		PushNotificationService,
 		QueryService,
 		ReactionService,
+		ReactionsBufferingService,
 		RelayService,
 		RoleService,
 		S3Service,
@@ -487,6 +490,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		$PushNotificationService,
 		$QueryService,
 		$ReactionService,
+		$ReactionsBufferingService,
 		$RelayService,
 		$RoleService,
 		$S3Service,
@@ -633,6 +637,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		PushNotificationService,
 		QueryService,
 		ReactionService,
+		ReactionsBufferingService,
 		RelayService,
 		RoleService,
 		S3Service,
@@ -777,6 +782,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		$PushNotificationService,
 		$QueryService,
 		$ReactionService,
+		$ReactionsBufferingService,
 		$RelayService,
 		$RoleService,
 		$S3Service,
diff --git a/packages/backend/src/core/QueueService.ts b/packages/backend/src/core/QueueService.ts
index ddb90a051f..f35e456556 100644
--- a/packages/backend/src/core/QueueService.ts
+++ b/packages/backend/src/core/QueueService.ts
@@ -87,6 +87,12 @@ export class QueueService {
 			repeat: { pattern: '*/5 * * * *' },
 			removeOnComplete: true,
 		});
+
+		this.systemQueue.add('bakeBufferedReactions', {
+		}, {
+			repeat: { pattern: '0 0 * * *' },
+			removeOnComplete: true,
+		});
 	}
 
 	@bindThis
diff --git a/packages/backend/src/core/ReactionService.ts b/packages/backend/src/core/ReactionService.ts
index 371207c33a..5993c42a1f 100644
--- a/packages/backend/src/core/ReactionService.ts
+++ b/packages/backend/src/core/ReactionService.ts
@@ -4,7 +4,6 @@
  */
 
 import { Inject, Injectable } from '@nestjs/common';
-import * as Redis from 'ioredis';
 import { DI } from '@/di-symbols.js';
 import type { EmojisRepository, NoteReactionsRepository, UsersRepository, NotesRepository } from '@/models/_.js';
 import { IdentifiableError } from '@/misc/identifiable-error.js';
@@ -30,9 +29,10 @@ import { RoleService } from '@/core/RoleService.js';
 import { FeaturedService } from '@/core/FeaturedService.js';
 import { trackPromise } from '@/misc/promise-tracker.js';
 import { isQuote, isRenote } from '@/misc/is-renote.js';
+import { ReactionsBufferingService } from '@/core/ReactionsBufferingService.js';
+import { PER_NOTE_REACTION_USER_PAIR_CACHE_MAX } from '@/const.js';
 
 const FALLBACK = '\u2764';
-const PER_NOTE_REACTION_USER_PAIR_CACHE_MAX = 16;
 
 const legacies: Record<string, string> = {
 	'like': '👍',
@@ -71,9 +71,6 @@ const decodeCustomEmojiRegexp = /^:([\w+-]+)(?:@([\w.-]+))?:$/;
 @Injectable()
 export class ReactionService {
 	constructor(
-		@Inject(DI.redis)
-		private redisClient: Redis.Redis,
-
 		@Inject(DI.usersRepository)
 		private usersRepository: UsersRepository,
 
@@ -93,6 +90,7 @@ export class ReactionService {
 		private userEntityService: UserEntityService,
 		private noteEntityService: NoteEntityService,
 		private userBlockingService: UserBlockingService,
+		private reactionsBufferingService: ReactionsBufferingService,
 		private idService: IdService,
 		private featuredService: FeaturedService,
 		private globalEventService: GlobalEventService,
@@ -174,7 +172,6 @@ export class ReactionService {
 			reaction,
 		};
 
-		// Create reaction
 		try {
 			await this.noteReactionsRepository.insert(record);
 		} catch (e) {
@@ -198,16 +195,25 @@ export class ReactionService {
 		}
 
 		// Increment reactions count
-		const sql = `jsonb_set("reactions", '{${reaction}}', (COALESCE("reactions"->>'${reaction}', '0')::int + 1)::text::jsonb)`;
-		await this.notesRepository.createQueryBuilder().update()
-			.set({
-				reactions: () => sql,
-				...(note.reactionAndUserPairCache.length < PER_NOTE_REACTION_USER_PAIR_CACHE_MAX ? {
-					reactionAndUserPairCache: () => `array_append("reactionAndUserPairCache", '${user.id}/${reaction}')`,
-				} : {}),
-			})
-			.where('id = :id', { id: note.id })
-			.execute();
+		if (meta.enableReactionsBuffering) {
+			await this.reactionsBufferingService.create(note.id, user.id, reaction, note.reactionAndUserPairCache);
+
+			// for debugging
+			if (reaction === ':angry_ai:') {
+				this.reactionsBufferingService.bake();
+			}
+		} else {
+			const sql = `jsonb_set("reactions", '{${reaction}}', (COALESCE("reactions"->>'${reaction}', '0')::int + 1)::text::jsonb)`;
+			await this.notesRepository.createQueryBuilder().update()
+				.set({
+					reactions: () => sql,
+					...(note.reactionAndUserPairCache.length < PER_NOTE_REACTION_USER_PAIR_CACHE_MAX ? {
+						reactionAndUserPairCache: () => `array_append("reactionAndUserPairCache", '${user.id}/${reaction}')`,
+					} : {}),
+				})
+				.where('id = :id', { id: note.id })
+				.execute();
+		}
 
 		// 30%の確率、セルフではない、3日以内に投稿されたノートの場合ハイライト用ランキング更新
 		if (
@@ -304,15 +310,21 @@ export class ReactionService {
 			throw new IdentifiableError('60527ec9-b4cb-4a88-a6bd-32d3ad26817d', 'not reacted');
 		}
 
+		const meta = await this.metaService.fetch();
+
 		// Decrement reactions count
-		const sql = `jsonb_set("reactions", '{${exist.reaction}}', (COALESCE("reactions"->>'${exist.reaction}', '0')::int - 1)::text::jsonb)`;
-		await this.notesRepository.createQueryBuilder().update()
-			.set({
-				reactions: () => sql,
-				reactionAndUserPairCache: () => `array_remove("reactionAndUserPairCache", '${user.id}/${exist.reaction}')`,
-			})
-			.where('id = :id', { id: note.id })
-			.execute();
+		if (meta.enableReactionsBuffering) {
+			await this.reactionsBufferingService.delete(note.id, user.id, exist.reaction);
+		} else {
+			const sql = `jsonb_set("reactions", '{${exist.reaction}}', (COALESCE("reactions"->>'${exist.reaction}', '0')::int - 1)::text::jsonb)`;
+			await this.notesRepository.createQueryBuilder().update()
+				.set({
+					reactions: () => sql,
+					reactionAndUserPairCache: () => `array_remove("reactionAndUserPairCache", '${user.id}/${exist.reaction}')`,
+				})
+				.where('id = :id', { id: note.id })
+				.execute();
+		}
 
 		this.globalEventService.publishNoteStream(note.id, 'unreacted', {
 			reaction: this.decodeReaction(exist.reaction).reaction,
diff --git a/packages/backend/src/core/ReactionsBufferingService.ts b/packages/backend/src/core/ReactionsBufferingService.ts
new file mode 100644
index 0000000000..b1a197feeb
--- /dev/null
+++ b/packages/backend/src/core/ReactionsBufferingService.ts
@@ -0,0 +1,162 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { Inject, Injectable } from '@nestjs/common';
+import * as Redis from 'ioredis';
+import { DI } from '@/di-symbols.js';
+import type { MiNote } from '@/models/Note.js';
+import { bindThis } from '@/decorators.js';
+import type { MiUser, NotesRepository } from '@/models/_.js';
+import type { Config } from '@/config.js';
+import { PER_NOTE_REACTION_USER_PAIR_CACHE_MAX } from '@/const.js';
+
+const REDIS_DELTA_PREFIX = 'reactionsBufferDeltas';
+const REDIS_PAIR_PREFIX = 'reactionsBufferPairs';
+
+@Injectable()
+export class ReactionsBufferingService {
+	constructor(
+		@Inject(DI.config)
+		private config: Config,
+
+		@Inject(DI.redisForReactions)
+		private redisForReactions: Redis.Redis, // TODO: 専用のRedisインスタンスにする
+
+		@Inject(DI.notesRepository)
+		private notesRepository: NotesRepository,
+	) {
+	}
+
+	@bindThis
+	public async create(noteId: MiNote['id'], userId: MiUser['id'], reaction: string, currentPairs: string[]): Promise<void> {
+		const pipeline = this.redisForReactions.pipeline();
+		pipeline.hincrby(`${REDIS_DELTA_PREFIX}:${noteId}`, reaction, 1);
+		for (let i = 0; i < currentPairs.length; i++) {
+			pipeline.zadd(`${REDIS_PAIR_PREFIX}:${noteId}`, i, currentPairs[i]);
+		}
+		pipeline.zadd(`${REDIS_PAIR_PREFIX}:${noteId}`, Date.now(), `${userId}/${reaction}`);
+		pipeline.zremrangebyrank(`${REDIS_PAIR_PREFIX}:${noteId}`, 0, -(PER_NOTE_REACTION_USER_PAIR_CACHE_MAX + 1));
+		await pipeline.exec();
+	}
+
+	@bindThis
+	public async delete(noteId: MiNote['id'], userId: MiUser['id'], reaction: string): Promise<void> {
+		const pipeline = this.redisForReactions.pipeline();
+		pipeline.hincrby(`${REDIS_DELTA_PREFIX}:${noteId}`, reaction, -1);
+		pipeline.zrem(`${REDIS_PAIR_PREFIX}:${noteId}`, `${userId}/${reaction}`);
+		// TODO: 「消した要素一覧」も持っておかないとcreateされた時に上書きされて復活する
+		await pipeline.exec();
+	}
+
+	@bindThis
+	public async get(noteId: MiNote['id']): Promise<{
+		deltas: Record<string, number>;
+		pairs: ([MiUser['id'], string])[];
+	}> {
+		const pipeline = this.redisForReactions.pipeline();
+		pipeline.hgetall(`${REDIS_DELTA_PREFIX}:${noteId}`);
+		pipeline.zrange(`${REDIS_PAIR_PREFIX}:${noteId}`, 0, -1);
+		const results = await pipeline.exec();
+
+		const resultDeltas = results![0][1] as Record<string, string>;
+		const resultPairs = results![1][1] as string[];
+
+		const deltas = {} as Record<string, number>;
+		for (const [name, count] of Object.entries(resultDeltas)) {
+			deltas[name] = parseInt(count);
+		}
+
+		const pairs = resultPairs.map(x => x.split('/') as [MiUser['id'], string]);
+
+		return {
+			deltas,
+			pairs,
+		};
+	}
+
+	@bindThis
+	public async getMany(noteIds: MiNote['id'][]): Promise<Map<MiNote['id'], {
+		deltas: Record<string, number>;
+		pairs: ([MiUser['id'], string])[];
+	}>> {
+		const map = new Map<MiNote['id'], {
+			deltas: Record<string, number>;
+			pairs: ([MiUser['id'], string])[];
+		}>();
+
+		const pipeline = this.redisForReactions.pipeline();
+		for (const noteId of noteIds) {
+			pipeline.hgetall(`${REDIS_DELTA_PREFIX}:${noteId}`);
+			pipeline.zrange(`${REDIS_PAIR_PREFIX}:${noteId}`, 0, -1);
+		}
+		const results = await pipeline.exec();
+
+		const opsForEachNotes = 2;
+		for (let i = 0; i < noteIds.length; i++) {
+			const noteId = noteIds[i];
+			const resultDeltas = results![i * opsForEachNotes][1] as Record<string, string>;
+			const resultPairs = results![i * opsForEachNotes + 1][1] as string[];
+
+			const deltas = {} as Record<string, number>;
+			for (const [name, count] of Object.entries(resultDeltas)) {
+				deltas[name] = parseInt(count);
+			}
+
+			const pairs = resultPairs.map(x => x.split('/') as [MiUser['id'], string]);
+
+			map.set(noteId, {
+				deltas,
+				pairs,
+			});
+		}
+
+		return map;
+	}
+
+	// TODO: scanは重い可能性があるので、別途 bufferedNoteIds を直接Redis上に持っておいてもいいかもしれない
+	@bindThis
+	public async bake(): Promise<void> {
+		const bufferedNoteIds = [];
+		let cursor = '0';
+		do {
+			// https://github.com/redis/ioredis#transparent-key-prefixing
+			const result = await this.redisForReactions.scan(
+				cursor,
+				'MATCH',
+				`${this.config.redis.prefix}:${REDIS_DELTA_PREFIX}:*`,
+				'COUNT',
+				'1000');
+
+			cursor = result[0];
+			bufferedNoteIds.push(...result[1].map(x => x.replace(`${this.config.redis.prefix}:${REDIS_DELTA_PREFIX}:`, '')));
+		} while (cursor !== '0');
+
+		const bufferedMap = await this.getMany(bufferedNoteIds);
+
+		// clear
+		const pipeline = this.redisForReactions.pipeline();
+		for (const noteId of bufferedNoteIds) {
+			pipeline.del(`${REDIS_DELTA_PREFIX}:${noteId}`);
+			pipeline.del(`${REDIS_PAIR_PREFIX}:${noteId}`);
+		}
+		await pipeline.exec();
+
+		// TODO: SQL一個にまとめたい
+		for (const [noteId, buffered] of bufferedMap) {
+			const sql = Object.entries(buffered.deltas)
+				.map(([reaction, count]) =>
+					`jsonb_set("reactions", '{${reaction}}', (COALESCE("reactions"->>'${reaction}', '0')::int + ${count})::text::jsonb)`)
+				.join(' || ');
+
+			this.notesRepository.createQueryBuilder().update()
+				.set({
+					reactions: () => sql,
+					reactionAndUserPairCache: buffered.pairs.map(x => x.join('/')),
+				})
+				.where('id = :id', { id: noteId })
+				.execute();
+		}
+	}
+}
diff --git a/packages/backend/src/core/entities/NoteEntityService.ts b/packages/backend/src/core/entities/NoteEntityService.ts
index 2cd092231c..7506d804c3 100644
--- a/packages/backend/src/core/entities/NoteEntityService.ts
+++ b/packages/backend/src/core/entities/NoteEntityService.ts
@@ -11,24 +11,39 @@ import type { Packed } from '@/misc/json-schema.js';
 import { awaitAll } from '@/misc/prelude/await-all.js';
 import type { MiUser } from '@/models/User.js';
 import type { MiNote } from '@/models/Note.js';
-import type { MiNoteReaction } from '@/models/NoteReaction.js';
 import type { UsersRepository, NotesRepository, FollowingsRepository, PollsRepository, PollVotesRepository, NoteReactionsRepository, ChannelsRepository } from '@/models/_.js';
 import { bindThis } from '@/decorators.js';
 import { DebounceLoader } from '@/misc/loader.js';
 import { IdService } from '@/core/IdService.js';
+import { ReactionsBufferingService } from '@/core/ReactionsBufferingService.js';
+import { MetaService } from '@/core/MetaService.js';
 import type { OnModuleInit } from '@nestjs/common';
 import type { CustomEmojiService } from '../CustomEmojiService.js';
 import type { ReactionService } from '../ReactionService.js';
 import type { UserEntityService } from './UserEntityService.js';
 import type { DriveFileEntityService } from './DriveFileEntityService.js';
 
+function mergeReactions(src: Record<string, number>, delta: Record<string, number>) {
+	const reactions = { ...src };
+	for (const [name, count] of Object.entries(delta)) {
+		if (reactions[name] != null) {
+			reactions[name] += count;
+		} else {
+			reactions[name] = count;
+		}
+	}
+	return reactions;
+}
+
 @Injectable()
 export class NoteEntityService implements OnModuleInit {
 	private userEntityService: UserEntityService;
 	private driveFileEntityService: DriveFileEntityService;
 	private customEmojiService: CustomEmojiService;
 	private reactionService: ReactionService;
+	private reactionsBufferingService: ReactionsBufferingService;
 	private idService: IdService;
+	private metaService: MetaService;
 	private noteLoader = new DebounceLoader(this.findNoteOrFail);
 
 	constructor(
@@ -59,6 +74,9 @@ export class NoteEntityService implements OnModuleInit {
 		//private driveFileEntityService: DriveFileEntityService,
 		//private customEmojiService: CustomEmojiService,
 		//private reactionService: ReactionService,
+		//private reactionsBufferingService: ReactionsBufferingService,
+		//private idService: IdService,
+		//private metaService: MetaService,
 	) {
 	}
 
@@ -67,7 +85,9 @@ export class NoteEntityService implements OnModuleInit {
 		this.driveFileEntityService = this.moduleRef.get('DriveFileEntityService');
 		this.customEmojiService = this.moduleRef.get('CustomEmojiService');
 		this.reactionService = this.moduleRef.get('ReactionService');
+		this.reactionsBufferingService = this.moduleRef.get('ReactionsBufferingService');
 		this.idService = this.moduleRef.get('IdService');
+		this.metaService = this.moduleRef.get('MetaService');
 	}
 
 	@bindThis
@@ -287,6 +307,7 @@ export class NoteEntityService implements OnModuleInit {
 			skipHide?: boolean;
 			withReactionAndUserPairCache?: boolean;
 			_hint_?: {
+				bufferdReactions: Map<MiNote['id'], { deltas: Record<string, number>; pairs: ([MiUser['id'], string])[] }> | null;
 				myReactions: Map<MiNote['id'], string | null>;
 				packedFiles: Map<MiNote['fileIds'][number], Packed<'DriveFile'> | null>;
 				packedUsers: Map<MiUser['id'], Packed<'UserLite'>>
@@ -303,6 +324,16 @@ export class NoteEntityService implements OnModuleInit {
 		const note = typeof src === 'object' ? src : await this.noteLoader.load(src);
 		const host = note.userHost;
 
+		const bufferdReactions = opts._hint_?.bufferdReactions != null ? (opts._hint_.bufferdReactions.get(note.id) ?? { deltas: {}, pairs: [] }) : await this.reactionsBufferingService.get(note.id);
+		const reactions = mergeReactions(note.reactions, bufferdReactions.deltas ?? {});
+		for (const [name, count] of Object.entries(reactions)) {
+			if (count <= 0) {
+				delete reactions[name];
+			}
+		}
+
+		const reactionAndUserPairCache = note.reactionAndUserPairCache.concat(bufferdReactions.pairs.map(x => x.join('/')));
+
 		let text = note.text;
 
 		if (note.name && (note.url ?? note.uri)) {
@@ -315,7 +346,7 @@ export class NoteEntityService implements OnModuleInit {
 				: await this.channelsRepository.findOneBy({ id: note.channelId })
 			: null;
 
-		const reactionEmojiNames = Object.keys(note.reactions)
+		const reactionEmojiNames = Object.keys(reactions)
 			.filter(x => x.startsWith(':') && x.includes('@') && !x.includes('@.')) // リモートカスタム絵文字のみ
 			.map(x => this.reactionService.decodeReaction(x).reaction.replaceAll(':', ''));
 		const packedFiles = options?._hint_?.packedFiles;
@@ -334,10 +365,10 @@ export class NoteEntityService implements OnModuleInit {
 			visibleUserIds: note.visibility === 'specified' ? note.visibleUserIds : undefined,
 			renoteCount: note.renoteCount,
 			repliesCount: note.repliesCount,
-			reactionCount: Object.values(note.reactions).reduce((a, b) => a + b, 0),
-			reactions: this.reactionService.convertLegacyReactions(note.reactions),
+			reactionCount: Object.values(reactions).reduce((a, b) => a + b, 0),
+			reactions: reactions,
 			reactionEmojis: this.customEmojiService.populateEmojis(reactionEmojiNames, host),
-			reactionAndUserPairCache: opts.withReactionAndUserPairCache ? note.reactionAndUserPairCache : undefined,
+			reactionAndUserPairCache: opts.withReactionAndUserPairCache ? reactionAndUserPairCache : undefined,
 			emojis: host != null ? this.customEmojiService.populateEmojis(note.emojis, host) : undefined,
 			tags: note.tags.length > 0 ? note.tags : undefined,
 			fileIds: note.fileIds,
@@ -376,8 +407,12 @@ export class NoteEntityService implements OnModuleInit {
 
 				poll: note.hasPoll ? this.populatePoll(note, meId) : undefined,
 
-				...(meId && Object.keys(note.reactions).length > 0 ? {
-					myReaction: this.populateMyReaction(note, meId, options?._hint_),
+				...(meId && Object.keys(reactions).length > 0 ? {
+					myReaction: this.populateMyReaction({
+						id: note.id,
+						reactions: reactions,
+						reactionAndUserPairCache: reactionAndUserPairCache,
+					}, meId, options?._hint_),
 				} : {}),
 			} : {}),
 		});
@@ -400,6 +435,10 @@ export class NoteEntityService implements OnModuleInit {
 	) {
 		if (notes.length === 0) return [];
 
+		const meta = await this.metaService.fetch();
+
+		const bufferdReactions = meta.enableReactionsBuffering ? await this.reactionsBufferingService.getMany(notes.map(x => x.id)) : null;
+
 		const meId = me ? me.id : null;
 		const myReactionsMap = new Map<MiNote['id'], string | null>();
 		if (meId) {
@@ -410,23 +449,33 @@ export class NoteEntityService implements OnModuleInit {
 
 			for (const note of notes) {
 				if (note.renote && (note.text == null && note.fileIds.length === 0)) { // pure renote
-					const reactionsCount = Object.values(note.renote.reactions).reduce((a, b) => a + b, 0);
+					const reactionsCount = Object.values(mergeReactions(note.renote.reactions, bufferdReactions?.get(note.renote.id)?.deltas ?? {})).reduce((a, b) => a + b, 0);
 					if (reactionsCount === 0) {
 						myReactionsMap.set(note.renote.id, null);
-					} else if (reactionsCount <= note.renote.reactionAndUserPairCache.length) {
-						const pair = note.renote.reactionAndUserPairCache.find(p => p.startsWith(meId));
-						myReactionsMap.set(note.renote.id, pair ? pair.split('/')[1] : null);
+					} else if (reactionsCount <= note.renote.reactionAndUserPairCache.length + (bufferdReactions?.get(note.renote.id)?.pairs.length ?? 0)) {
+						const pairInBuffer = bufferdReactions?.get(note.renote.id)?.pairs.find(p => p[0] === meId);
+						if (pairInBuffer) {
+							myReactionsMap.set(note.renote.id, pairInBuffer[1]);
+						} else {
+							const pair = note.renote.reactionAndUserPairCache.find(p => p.startsWith(meId));
+							myReactionsMap.set(note.renote.id, pair ? pair.split('/')[1] : null);
+						}
 					} else {
 						idsNeedFetchMyReaction.add(note.renote.id);
 					}
 				} else {
 					if (note.id < oldId) {
-						const reactionsCount = Object.values(note.reactions).reduce((a, b) => a + b, 0);
+						const reactionsCount = Object.values(mergeReactions(note.reactions, bufferdReactions?.get(note.id)?.deltas ?? {})).reduce((a, b) => a + b, 0);
 						if (reactionsCount === 0) {
 							myReactionsMap.set(note.id, null);
-						} else if (reactionsCount <= note.reactionAndUserPairCache.length) {
-							const pair = note.reactionAndUserPairCache.find(p => p.startsWith(meId));
-							myReactionsMap.set(note.id, pair ? pair.split('/')[1] : null);
+						} else if (reactionsCount <= note.reactionAndUserPairCache.length + (bufferdReactions?.get(note.id)?.pairs.length ?? 0)) {
+							const pairInBuffer = bufferdReactions?.get(note.id)?.pairs.find(p => p[0] === meId);
+							if (pairInBuffer) {
+								myReactionsMap.set(note.id, pairInBuffer[1]);
+							} else {
+								const pair = note.reactionAndUserPairCache.find(p => p.startsWith(meId));
+								myReactionsMap.set(note.id, pair ? pair.split('/')[1] : null);
+							}
 						} else {
 							idsNeedFetchMyReaction.add(note.id);
 						}
@@ -461,6 +510,7 @@ export class NoteEntityService implements OnModuleInit {
 		return await Promise.all(notes.map(n => this.pack(n, me, {
 			...options,
 			_hint_: {
+				bufferdReactions,
 				myReactions: myReactionsMap,
 				packedFiles,
 				packedUsers,
diff --git a/packages/backend/src/di-symbols.ts b/packages/backend/src/di-symbols.ts
index 271082b4ff..b6f003c2e6 100644
--- a/packages/backend/src/di-symbols.ts
+++ b/packages/backend/src/di-symbols.ts
@@ -11,6 +11,7 @@ export const DI = {
 	redisForPub: Symbol('redisForPub'),
 	redisForSub: Symbol('redisForSub'),
 	redisForTimelines: Symbol('redisForTimelines'),
+	redisForReactions: Symbol('redisForReactions'),
 
 	//#region Repositories
 	usersRepository: Symbol('usersRepository'),
diff --git a/packages/backend/src/models/Meta.ts b/packages/backend/src/models/Meta.ts
index 70d41801b5..9ab76d373f 100644
--- a/packages/backend/src/models/Meta.ts
+++ b/packages/backend/src/models/Meta.ts
@@ -589,6 +589,11 @@ export class MiMeta {
 	})
 	public perUserListTimelineCacheMax: number;
 
+	@Column('boolean', {
+		default: false,
+	})
+	public enableReactionsBuffering: boolean;
+
 	@Column('integer', {
 		default: 0,
 	})
diff --git a/packages/backend/src/queue/QueueProcessorModule.ts b/packages/backend/src/queue/QueueProcessorModule.ts
index a1fd38fcc5..0027b5ef3d 100644
--- a/packages/backend/src/queue/QueueProcessorModule.ts
+++ b/packages/backend/src/queue/QueueProcessorModule.ts
@@ -14,6 +14,7 @@ import { InboxProcessorService } from './processors/InboxProcessorService.js';
 import { UserWebhookDeliverProcessorService } from './processors/UserWebhookDeliverProcessorService.js';
 import { SystemWebhookDeliverProcessorService } from './processors/SystemWebhookDeliverProcessorService.js';
 import { CheckExpiredMutingsProcessorService } from './processors/CheckExpiredMutingsProcessorService.js';
+import { BakeBufferedReactionsProcessorService } from './processors/BakeBufferedReactionsProcessorService.js';
 import { CleanChartsProcessorService } from './processors/CleanChartsProcessorService.js';
 import { CleanProcessorService } from './processors/CleanProcessorService.js';
 import { CleanRemoteFilesProcessorService } from './processors/CleanRemoteFilesProcessorService.js';
@@ -51,6 +52,7 @@ import { RelationshipProcessorService } from './processors/RelationshipProcessor
 		ResyncChartsProcessorService,
 		CleanChartsProcessorService,
 		CheckExpiredMutingsProcessorService,
+		BakeBufferedReactionsProcessorService,
 		CleanProcessorService,
 		DeleteDriveFilesProcessorService,
 		ExportCustomEmojisProcessorService,
diff --git a/packages/backend/src/queue/QueueProcessorService.ts b/packages/backend/src/queue/QueueProcessorService.ts
index 7bd74f3210..e9e1c45224 100644
--- a/packages/backend/src/queue/QueueProcessorService.ts
+++ b/packages/backend/src/queue/QueueProcessorService.ts
@@ -39,6 +39,7 @@ import { TickChartsProcessorService } from './processors/TickChartsProcessorServ
 import { ResyncChartsProcessorService } from './processors/ResyncChartsProcessorService.js';
 import { CleanChartsProcessorService } from './processors/CleanChartsProcessorService.js';
 import { CheckExpiredMutingsProcessorService } from './processors/CheckExpiredMutingsProcessorService.js';
+import { BakeBufferedReactionsProcessorService } from './processors/BakeBufferedReactionsProcessorService.js';
 import { CleanProcessorService } from './processors/CleanProcessorService.js';
 import { AggregateRetentionProcessorService } from './processors/AggregateRetentionProcessorService.js';
 import { QueueLoggerService } from './QueueLoggerService.js';
@@ -118,6 +119,7 @@ export class QueueProcessorService implements OnApplicationShutdown {
 		private cleanChartsProcessorService: CleanChartsProcessorService,
 		private aggregateRetentionProcessorService: AggregateRetentionProcessorService,
 		private checkExpiredMutingsProcessorService: CheckExpiredMutingsProcessorService,
+		private bakeBufferedReactionsProcessorService: BakeBufferedReactionsProcessorService,
 		private cleanProcessorService: CleanProcessorService,
 	) {
 		this.logger = this.queueLoggerService.logger;
@@ -147,6 +149,7 @@ export class QueueProcessorService implements OnApplicationShutdown {
 					case 'cleanCharts': return this.cleanChartsProcessorService.process();
 					case 'aggregateRetention': return this.aggregateRetentionProcessorService.process();
 					case 'checkExpiredMutings': return this.checkExpiredMutingsProcessorService.process();
+					case 'bakeBufferedReactions': return this.bakeBufferedReactionsProcessorService.process();
 					case 'clean': return this.cleanProcessorService.process();
 					default: throw new Error(`unrecognized job type ${job.name} for system`);
 				}
diff --git a/packages/backend/src/queue/processors/BakeBufferedReactionsProcessorService.ts b/packages/backend/src/queue/processors/BakeBufferedReactionsProcessorService.ts
new file mode 100644
index 0000000000..cd56ba9837
--- /dev/null
+++ b/packages/backend/src/queue/processors/BakeBufferedReactionsProcessorService.ts
@@ -0,0 +1,40 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { Inject, Injectable } from '@nestjs/common';
+import type Logger from '@/logger.js';
+import { bindThis } from '@/decorators.js';
+import { ReactionsBufferingService } from '@/core/ReactionsBufferingService.js';
+import { MetaService } from '@/core/MetaService.js';
+import { QueueLoggerService } from '../QueueLoggerService.js';
+import type * as Bull from 'bullmq';
+
+@Injectable()
+export class BakeBufferedReactionsProcessorService {
+	private logger: Logger;
+
+	constructor(
+		private reactionsBufferingService: ReactionsBufferingService,
+		private metaService: MetaService,
+		private queueLoggerService: QueueLoggerService,
+	) {
+		this.logger = this.queueLoggerService.logger.createSubLogger('bake-buffered-reactions');
+	}
+
+	@bindThis
+	public async process(): Promise<void> {
+		const meta = await this.metaService.fetch();
+		if (!meta.enableReactionsBuffering) {
+			this.logger.info('Reactions buffering is disabled. Skipping...');
+			return;
+		}
+
+		this.logger.info('Baking buffered reactions...');
+
+		await this.reactionsBufferingService.bake();
+
+		this.logger.succ('All buffered reactions baked.');
+	}
+}
diff --git a/packages/backend/src/server/HealthServerService.ts b/packages/backend/src/server/HealthServerService.ts
index 2c3ed85925..5980609f02 100644
--- a/packages/backend/src/server/HealthServerService.ts
+++ b/packages/backend/src/server/HealthServerService.ts
@@ -27,6 +27,9 @@ export class HealthServerService {
 		@Inject(DI.redisForTimelines)
 		private redisForTimelines: Redis.Redis,
 
+		@Inject(DI.redisForReactions)
+		private redisForReactions: Redis.Redis,
+
 		@Inject(DI.db)
 		private db: DataSource,
 
@@ -43,6 +46,7 @@ export class HealthServerService {
 				this.redisForPub.ping(),
 				this.redisForSub.ping(),
 				this.redisForTimelines.ping(),
+				this.redisForReactions.ping(),
 				this.db.query('SELECT 1'),
 				...(this.meilisearch ? [this.meilisearch.health()] : []),
 			]).then(() => 200, () => 503));
diff --git a/packages/backend/src/server/api/endpoints/admin/meta.ts b/packages/backend/src/server/api/endpoints/admin/meta.ts
index 2e7f73da73..29e8bfaf14 100644
--- a/packages/backend/src/server/api/endpoints/admin/meta.ts
+++ b/packages/backend/src/server/api/endpoints/admin/meta.ts
@@ -377,6 +377,10 @@ export const meta = {
 				type: 'number',
 				optional: false, nullable: false,
 			},
+			enableReactionsBuffering: {
+				type: 'boolean',
+				optional: false, nullable: false,
+			},
 			notesPerOneAd: {
 				type: 'number',
 				optional: false, nullable: false,
@@ -617,6 +621,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				perRemoteUserUserTimelineCacheMax: instance.perRemoteUserUserTimelineCacheMax,
 				perUserHomeTimelineCacheMax: instance.perUserHomeTimelineCacheMax,
 				perUserListTimelineCacheMax: instance.perUserListTimelineCacheMax,
+				enableReactionsBuffering: instance.enableReactionsBuffering,
 				notesPerOneAd: instance.notesPerOneAd,
 				summalyProxy: instance.urlPreviewSummaryProxyUrl,
 				urlPreviewEnabled: instance.urlPreviewEnabled,
diff --git a/packages/backend/src/server/api/endpoints/admin/update-meta.ts b/packages/backend/src/server/api/endpoints/admin/update-meta.ts
index 5efdc9d8c4..865e73f274 100644
--- a/packages/backend/src/server/api/endpoints/admin/update-meta.ts
+++ b/packages/backend/src/server/api/endpoints/admin/update-meta.ts
@@ -142,6 +142,7 @@ export const paramDef = {
 		perRemoteUserUserTimelineCacheMax: { type: 'integer' },
 		perUserHomeTimelineCacheMax: { type: 'integer' },
 		perUserListTimelineCacheMax: { type: 'integer' },
+		enableReactionsBuffering: { type: 'boolean' },
 		notesPerOneAd: { type: 'integer' },
 		silencedHosts: {
 			type: 'array',
@@ -598,6 +599,10 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				set.perUserListTimelineCacheMax = ps.perUserListTimelineCacheMax;
 			}
 
+			if (ps.enableReactionsBuffering !== undefined) {
+				set.enableReactionsBuffering = ps.enableReactionsBuffering;
+			}
+
 			if (ps.notesPerOneAd !== undefined) {
 				set.notesPerOneAd = ps.notesPerOneAd;
 			}
diff --git a/packages/backend/test/unit/entities/UserEntityService.ts b/packages/backend/test/unit/entities/UserEntityService.ts
index ee16d421c4..e4f42809f8 100644
--- a/packages/backend/test/unit/entities/UserEntityService.ts
+++ b/packages/backend/test/unit/entities/UserEntityService.ts
@@ -4,10 +4,10 @@
  */
 
 import { Test, TestingModule } from '@nestjs/testing';
+import type { MiUser } from '@/models/User.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
 import { GlobalModule } from '@/GlobalModule.js';
 import { CoreModule } from '@/core/CoreModule.js';
-import type { MiUser } from '@/models/User.js';
 import { secureRndstr } from '@/misc/secure-rndstr.js';
 import { genAidx } from '@/misc/id/aidx.js';
 import {
@@ -49,6 +49,7 @@ import { ApLoggerService } from '@/core/activitypub/ApLoggerService.js';
 import { AccountMoveService } from '@/core/AccountMoveService.js';
 import { ReactionService } from '@/core/ReactionService.js';
 import { NotificationService } from '@/core/NotificationService.js';
+import { ReactionsBufferingService } from '@/core/ReactionsBufferingService.js';
 
 process.env.NODE_ENV = 'test';
 
@@ -169,6 +170,7 @@ describe('UserEntityService', () => {
 				ApLoggerService,
 				AccountMoveService,
 				ReactionService,
+				ReactionsBufferingService,
 				NotificationService,
 			];
 
diff --git a/packages/frontend/src/pages/admin/other-settings.vue b/packages/frontend/src/pages/admin/other-settings.vue
index 345cf333b5..0163daf1ba 100644
--- a/packages/frontend/src/pages/admin/other-settings.vue
+++ b/packages/frontend/src/pages/admin/other-settings.vue
@@ -36,6 +36,55 @@ SPDX-License-Identifier: AGPL-3.0-only
 						<template #caption>{{ i18n.ts.turnOffToImprovePerformance }}</template>
 					</MkSwitch>
 				</div>
+
+				<MkFolder :defaultOpen="true">
+					<template #icon><i class="ti ti-bolt"></i></template>
+					<template #label>Misskey® Fan-out Timeline Technology™ (FTT)</template>
+					<template v-if="enableFanoutTimeline" #suffix>Enabled</template>
+					<template v-else #suffix>Disabled</template>
+
+					<div class="_gaps_m">
+						<MkSwitch v-model="enableFanoutTimeline">
+							<template #label>{{ i18n.ts.enable }}</template>
+							<template #caption>{{ i18n.ts._serverSettings.fanoutTimelineDescription }}</template>
+						</MkSwitch>
+
+						<MkSwitch v-model="enableFanoutTimelineDbFallback">
+							<template #label>{{ i18n.ts._serverSettings.fanoutTimelineDbFallback }}</template>
+							<template #caption>{{ i18n.ts._serverSettings.fanoutTimelineDbFallbackDescription }}</template>
+						</MkSwitch>
+
+						<MkInput v-model="perLocalUserUserTimelineCacheMax" type="number">
+							<template #label>perLocalUserUserTimelineCacheMax</template>
+						</MkInput>
+
+						<MkInput v-model="perRemoteUserUserTimelineCacheMax" type="number">
+							<template #label>perRemoteUserUserTimelineCacheMax</template>
+						</MkInput>
+
+						<MkInput v-model="perUserHomeTimelineCacheMax" type="number">
+							<template #label>perUserHomeTimelineCacheMax</template>
+						</MkInput>
+
+						<MkInput v-model="perUserListTimelineCacheMax" type="number">
+							<template #label>perUserListTimelineCacheMax</template>
+						</MkInput>
+					</div>
+				</MkFolder>
+
+				<MkFolder :defaultOpen="true">
+					<template #icon><i class="ti ti-bolt"></i></template>
+					<template #label>Misskey® Reactions Buffering Technology™ (RBT)<span class="_beta">{{ i18n.ts.beta }}</span></template>
+					<template v-if="enableReactionsBuffering" #suffix>Enabled</template>
+					<template v-else #suffix>Disabled</template>
+
+					<div class="_gaps_m">
+						<MkSwitch v-model="enableReactionsBuffering">
+							<template #label>{{ i18n.ts.enable }}</template>
+							<template #caption>{{ i18n.ts._serverSettings.reactionsBufferingDescription }}</template>
+						</MkSwitch>
+					</div>
+				</MkFolder>
 			</div>
 		</FormSuspense>
 	</MkSpacer>
@@ -52,11 +101,20 @@ import { fetchInstance } from '@/instance.js';
 import { i18n } from '@/i18n.js';
 import { definePageMetadata } from '@/scripts/page-metadata.js';
 import MkSwitch from '@/components/MkSwitch.vue';
+import MkFolder from '@/components/MkFolder.vue';
+import MkInput from '@/components/MkInput.vue';
 
 const enableServerMachineStats = ref<boolean>(false);
 const enableIdenticonGeneration = ref<boolean>(false);
 const enableChartsForRemoteUser = ref<boolean>(false);
 const enableChartsForFederatedInstances = ref<boolean>(false);
+const enableFanoutTimeline = ref<boolean>(false);
+const enableFanoutTimelineDbFallback = ref<boolean>(false);
+const perLocalUserUserTimelineCacheMax = ref<number>(0);
+const perRemoteUserUserTimelineCacheMax = ref<number>(0);
+const perUserHomeTimelineCacheMax = ref<number>(0);
+const perUserListTimelineCacheMax = ref<number>(0);
+const enableReactionsBuffering = ref<boolean>(false);
 
 async function init() {
 	const meta = await misskeyApi('admin/meta');
@@ -64,6 +122,13 @@ async function init() {
 	enableIdenticonGeneration.value = meta.enableIdenticonGeneration;
 	enableChartsForRemoteUser.value = meta.enableChartsForRemoteUser;
 	enableChartsForFederatedInstances.value = meta.enableChartsForFederatedInstances;
+	enableFanoutTimeline.value = meta.enableFanoutTimeline;
+	enableFanoutTimelineDbFallback.value = meta.enableFanoutTimelineDbFallback;
+	perLocalUserUserTimelineCacheMax.value = meta.perLocalUserUserTimelineCacheMax;
+	perRemoteUserUserTimelineCacheMax.value = meta.perRemoteUserUserTimelineCacheMax;
+	perUserHomeTimelineCacheMax.value = meta.perUserHomeTimelineCacheMax;
+	perUserListTimelineCacheMax.value = meta.perUserListTimelineCacheMax;
+	enableReactionsBuffering.value = meta.enableReactionsBuffering;
 }
 
 function save() {
@@ -72,6 +137,13 @@ function save() {
 		enableIdenticonGeneration: enableIdenticonGeneration.value,
 		enableChartsForRemoteUser: enableChartsForRemoteUser.value,
 		enableChartsForFederatedInstances: enableChartsForFederatedInstances.value,
+		enableFanoutTimeline: enableFanoutTimeline.value,
+		enableFanoutTimelineDbFallback: enableFanoutTimelineDbFallback.value,
+		perLocalUserUserTimelineCacheMax: perLocalUserUserTimelineCacheMax.value,
+		perRemoteUserUserTimelineCacheMax: perRemoteUserUserTimelineCacheMax.value,
+		perUserHomeTimelineCacheMax: perUserHomeTimelineCacheMax.value,
+		perUserListTimelineCacheMax: perUserListTimelineCacheMax.value,
+		enableReactionsBuffering: enableReactionsBuffering.value,
 	}).then(() => {
 		fetchInstance(true);
 	});
diff --git a/packages/frontend/src/pages/admin/settings.vue b/packages/frontend/src/pages/admin/settings.vue
index 6f45c212ec..ffff57b454 100644
--- a/packages/frontend/src/pages/admin/settings.vue
+++ b/packages/frontend/src/pages/admin/settings.vue
@@ -97,38 +97,6 @@ SPDX-License-Identifier: AGPL-3.0-only
 					</FormSection>
 
 					<FormSection>
-						<template #label>Misskey® Fan-out Timeline Technology™ (FTT)</template>
-
-						<div class="_gaps_m">
-							<MkSwitch v-model="enableFanoutTimeline">
-								<template #label>{{ i18n.ts.enable }}</template>
-								<template #caption>{{ i18n.ts._serverSettings.fanoutTimelineDescription }}</template>
-							</MkSwitch>
-
-							<MkSwitch v-model="enableFanoutTimelineDbFallback">
-								<template #label>{{ i18n.ts._serverSettings.fanoutTimelineDbFallback }}</template>
-								<template #caption>{{ i18n.ts._serverSettings.fanoutTimelineDbFallbackDescription }}</template>
-							</MkSwitch>
-
-							<MkInput v-model="perLocalUserUserTimelineCacheMax" type="number">
-								<template #label>perLocalUserUserTimelineCacheMax</template>
-							</MkInput>
-
-							<MkInput v-model="perRemoteUserUserTimelineCacheMax" type="number">
-								<template #label>perRemoteUserUserTimelineCacheMax</template>
-							</MkInput>
-
-							<MkInput v-model="perUserHomeTimelineCacheMax" type="number">
-								<template #label>perUserHomeTimelineCacheMax</template>
-							</MkInput>
-
-							<MkInput v-model="perUserListTimelineCacheMax" type="number">
-								<template #label>perUserListTimelineCacheMax</template>
-							</MkInput>
-						</div>
-					</FormSection>
-
-					<FormSection>
 						<template #label>{{ i18n.ts._ad.adsSettings }}</template>
 
 						<div class="_gaps_m">
@@ -236,12 +204,6 @@ const cacheRemoteSensitiveFiles = ref<boolean>(false);
 const enableServiceWorker = ref<boolean>(false);
 const swPublicKey = ref<string | null>(null);
 const swPrivateKey = ref<string | null>(null);
-const enableFanoutTimeline = ref<boolean>(false);
-const enableFanoutTimelineDbFallback = ref<boolean>(false);
-const perLocalUserUserTimelineCacheMax = ref<number>(0);
-const perRemoteUserUserTimelineCacheMax = ref<number>(0);
-const perUserHomeTimelineCacheMax = ref<number>(0);
-const perUserListTimelineCacheMax = ref<number>(0);
 const notesPerOneAd = ref<number>(0);
 const urlPreviewEnabled = ref<boolean>(true);
 const urlPreviewTimeout = ref<number>(10000);
@@ -265,12 +227,6 @@ async function init(): Promise<void> {
 	enableServiceWorker.value = meta.enableServiceWorker;
 	swPublicKey.value = meta.swPublickey;
 	swPrivateKey.value = meta.swPrivateKey;
-	enableFanoutTimeline.value = meta.enableFanoutTimeline;
-	enableFanoutTimelineDbFallback.value = meta.enableFanoutTimelineDbFallback;
-	perLocalUserUserTimelineCacheMax.value = meta.perLocalUserUserTimelineCacheMax;
-	perRemoteUserUserTimelineCacheMax.value = meta.perRemoteUserUserTimelineCacheMax;
-	perUserHomeTimelineCacheMax.value = meta.perUserHomeTimelineCacheMax;
-	perUserListTimelineCacheMax.value = meta.perUserListTimelineCacheMax;
 	notesPerOneAd.value = meta.notesPerOneAd;
 	urlPreviewEnabled.value = meta.urlPreviewEnabled;
 	urlPreviewTimeout.value = meta.urlPreviewTimeout;
@@ -295,12 +251,6 @@ async function save() {
 		enableServiceWorker: enableServiceWorker.value,
 		swPublicKey: swPublicKey.value,
 		swPrivateKey: swPrivateKey.value,
-		enableFanoutTimeline: enableFanoutTimeline.value,
-		enableFanoutTimelineDbFallback: enableFanoutTimelineDbFallback.value,
-		perLocalUserUserTimelineCacheMax: perLocalUserUserTimelineCacheMax.value,
-		perRemoteUserUserTimelineCacheMax: perRemoteUserUserTimelineCacheMax.value,
-		perUserHomeTimelineCacheMax: perUserHomeTimelineCacheMax.value,
-		perUserListTimelineCacheMax: perUserListTimelineCacheMax.value,
 		notesPerOneAd: notesPerOneAd.value,
 		urlPreviewEnabled: urlPreviewEnabled.value,
 		urlPreviewTimeout: urlPreviewTimeout.value,
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index 03828b6552..672d75e267 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -5125,6 +5125,7 @@ export type operations = {
             perRemoteUserUserTimelineCacheMax: number;
             perUserHomeTimelineCacheMax: number;
             perUserListTimelineCacheMax: number;
+            enableReactionsBuffering: boolean;
             notesPerOneAd: number;
             backgroundImageUrl: string | null;
             deeplAuthKey: string | null;
@@ -9395,6 +9396,7 @@ export type operations = {
           perRemoteUserUserTimelineCacheMax?: number;
           perUserHomeTimelineCacheMax?: number;
           perUserListTimelineCacheMax?: number;
+          enableReactionsBuffering?: boolean;
           notesPerOneAd?: number;
           silencedHosts?: string[] | null;
           mediaSilencedHosts?: string[] | null;