diff --git a/packages/backend/src/core/AvatarDecorationService.ts b/packages/backend/src/core/AvatarDecorationService.ts
index 21e31d79a4..fa3f63677e 100644
--- a/packages/backend/src/core/AvatarDecorationService.ts
+++ b/packages/backend/src/core/AvatarDecorationService.ts
@@ -29,7 +29,7 @@ export class AvatarDecorationService implements OnApplicationShutdown {
 		private moderationLogService: ModerationLogService,
 		private globalEventService: GlobalEventService,
 	) {
-		this.cache = new MemorySingleCache<MiAvatarDecoration[]>(1000 * 60 * 30);
+		this.cache = new MemorySingleCache<MiAvatarDecoration[]>(1000 * 60 * 30); // 30s
 
 		this.redisForSub.on('message', this.onMessage);
 	}
diff --git a/packages/backend/src/core/CacheService.ts b/packages/backend/src/core/CacheService.ts
index d008e7ec52..6725ebe75b 100644
--- a/packages/backend/src/core/CacheService.ts
+++ b/packages/backend/src/core/CacheService.ts
@@ -56,10 +56,10 @@ export class CacheService implements OnApplicationShutdown {
 	) {
 		//this.onMessage = this.onMessage.bind(this);
 
-		this.userByIdCache = new MemoryKVCache<MiUser>(Infinity);
-		this.localUserByNativeTokenCache = new MemoryKVCache<MiLocalUser | null>(Infinity);
-		this.localUserByIdCache = new MemoryKVCache<MiLocalUser>(Infinity);
-		this.uriPersonCache = new MemoryKVCache<MiUser | null>(Infinity);
+		this.userByIdCache = new MemoryKVCache<MiUser>(1000 * 60 * 5); // 5m
+		this.localUserByNativeTokenCache = new MemoryKVCache<MiLocalUser | null>(1000 * 60 * 5); // 5m
+		this.localUserByIdCache = new MemoryKVCache<MiLocalUser>(1000 * 60 * 5); // 5m
+		this.uriPersonCache = new MemoryKVCache<MiUser | null>(1000 * 60 * 5); // 5m
 
 		this.userProfileCache = new RedisKVCache<MiUserProfile>(this.redisClient, 'userProfile', {
 			lifetime: 1000 * 60 * 30, // 30m
@@ -135,14 +135,14 @@ export class CacheService implements OnApplicationShutdown {
 					if (user == null) {
 						this.userByIdCache.delete(body.id);
 						this.localUserByIdCache.delete(body.id);
-						for (const [k, v] of this.uriPersonCache.cache.entries()) {
+						for (const [k, v] of this.uriPersonCache.entries) {
 							if (v.value?.id === body.id) {
 								this.uriPersonCache.delete(k);
 							}
 						}
 					} else {
 						this.userByIdCache.set(user.id, user);
-						for (const [k, v] of this.uriPersonCache.cache.entries()) {
+						for (const [k, v] of this.uriPersonCache.entries) {
 							if (v.value?.id === user.id) {
 								this.uriPersonCache.set(k, user);
 							}
diff --git a/packages/backend/src/core/CustomEmojiService.ts b/packages/backend/src/core/CustomEmojiService.ts
index eea0f9228d..aa99261549 100644
--- a/packages/backend/src/core/CustomEmojiService.ts
+++ b/packages/backend/src/core/CustomEmojiService.ts
@@ -26,7 +26,7 @@ const parseEmojiStrRegexp = /^([-\w]+)(?:@([\w.-]+))?$/;
 
 @Injectable()
 export class CustomEmojiService implements OnApplicationShutdown {
-	private cache: MemoryKVCache<MiEmoji | null>;
+	private emojisCache: MemoryKVCache<MiEmoji | null>;
 	public localEmojisCache: RedisSingleCache<Map<string, MiEmoji>>;
 
 	constructor(
@@ -49,7 +49,7 @@ export class CustomEmojiService implements OnApplicationShutdown {
 		private globalEventService: GlobalEventService,
 		private driveService: DriveService,
 	) {
-		this.cache = new MemoryKVCache<MiEmoji | null>(1000 * 60 * 60 * 12);
+		this.emojisCache = new MemoryKVCache<MiEmoji | null>(1000 * 60 * 60 * 12); // 12h
 
 		this.localEmojisCache = new RedisSingleCache<Map<string, MiEmoji>>(this.redisClient, 'localEmojis', {
 			lifetime: 1000 * 60 * 30, // 30m
@@ -357,14 +357,14 @@ export class CustomEmojiService implements OnApplicationShutdown {
 		if (name == null) return null;
 		if (host == null) return null;
 
-		const newHost = host === this.config.host ? null : host; 
+		const newHost = host === this.config.host ? null : host;
 
 		const queryOrNull = async () => (await this.emojisRepository.findOneBy({
 			name,
 			host: newHost ?? IsNull(),
 		})) ?? null;
 
-		const emoji = await this.cache.fetch(`${name} ${host}`, queryOrNull);
+		const emoji = await this.emojisCache.fetch(`${name} ${host}`, queryOrNull);
 
 		if (emoji == null) return null;
 		return emoji.publicUrl || emoji.originalUrl; // || emoji.originalUrl してるのは後方互換性のため（publicUrlはstringなので??はだめ）
@@ -391,7 +391,7 @@ export class CustomEmojiService implements OnApplicationShutdown {
 	 */
 	@bindThis
 	public async prefetchEmojis(emojis: { name: string; host: string | null; }[]): Promise<void> {
-		const notCachedEmojis = emojis.filter(emoji => this.cache.get(`${emoji.name} ${emoji.host}`) == null);
+		const notCachedEmojis = emojis.filter(emoji => this.emojisCache.get(`${emoji.name} ${emoji.host}`) == null);
 		const emojisQuery: any[] = [];
 		const hosts = new Set(notCachedEmojis.map(e => e.host));
 		for (const host of hosts) {
@@ -406,7 +406,7 @@ export class CustomEmojiService implements OnApplicationShutdown {
 			select: ['name', 'host', 'originalUrl', 'publicUrl'],
 		}) : [];
 		for (const emoji of _emojis) {
-			this.cache.set(`${emoji.name} ${emoji.host}`, emoji);
+			this.emojisCache.set(`${emoji.name} ${emoji.host}`, emoji);
 		}
 	}
 
@@ -431,7 +431,7 @@ export class CustomEmojiService implements OnApplicationShutdown {
 
 	@bindThis
 	public dispose(): void {
-		this.cache.dispose();
+		this.emojisCache.dispose();
 	}
 
 	@bindThis
diff --git a/packages/backend/src/core/RelayService.ts b/packages/backend/src/core/RelayService.ts
index e9dc9b57af..91857dc683 100644
--- a/packages/backend/src/core/RelayService.ts
+++ b/packages/backend/src/core/RelayService.ts
@@ -35,7 +35,7 @@ export class RelayService {
 		private createSystemUserService: CreateSystemUserService,
 		private apRendererService: ApRendererService,
 	) {
-		this.relaysCache = new MemorySingleCache<MiRelay[]>(1000 * 60 * 10);
+		this.relaysCache = new MemorySingleCache<MiRelay[]>(1000 * 60 * 10); // 10m
 	}
 
 	@bindThis
diff --git a/packages/backend/src/core/RoleService.ts b/packages/backend/src/core/RoleService.ts
index f5a753afc7..2b6089fd3a 100644
--- a/packages/backend/src/core/RoleService.ts
+++ b/packages/backend/src/core/RoleService.ts
@@ -129,10 +129,8 @@ export class RoleService implements OnApplicationShutdown, OnModuleInit {
 		private moderationLogService: ModerationLogService,
 		private fanoutTimelineService: FanoutTimelineService,
 	) {
-		//this.onMessage = this.onMessage.bind(this);
-
-		this.rolesCache = new MemorySingleCache<MiRole[]>(1000 * 60 * 60 * 1);
-		this.roleAssignmentByUserIdCache = new MemoryKVCache<MiRoleAssignment[]>(1000 * 60 * 60 * 1);
+		this.rolesCache = new MemorySingleCache<MiRole[]>(1000 * 60 * 60); // 1h
+		this.roleAssignmentByUserIdCache = new MemoryKVCache<MiRoleAssignment[]>(1000 * 60 * 5); // 5m
 
 		this.redisForSub.on('message', this.onMessage);
 	}
diff --git a/packages/backend/src/core/UserKeypairService.ts b/packages/backend/src/core/UserKeypairService.ts
index 51ac99179a..92d61cd103 100644
--- a/packages/backend/src/core/UserKeypairService.ts
+++ b/packages/backend/src/core/UserKeypairService.ts
@@ -25,7 +25,7 @@ export class UserKeypairService implements OnApplicationShutdown {
 	) {
 		this.cache = new RedisKVCache<MiUserKeypair>(this.redisClient, 'userKeypair', {
 			lifetime: 1000 * 60 * 60 * 24, // 24h
-			memoryCacheLifetime: Infinity,
+			memoryCacheLifetime: 1000 * 60 * 60, // 1h
 			fetcher: (key) => this.userKeypairsRepository.findOneByOrFail({ userId: key }),
 			toRedisConverter: (value) => JSON.stringify(value),
 			fromRedisConverter: (value) => JSON.parse(value),
diff --git a/packages/backend/src/core/activitypub/ApDbResolverService.ts b/packages/backend/src/core/activitypub/ApDbResolverService.ts
index 44680a2ed5..062af39732 100644
--- a/packages/backend/src/core/activitypub/ApDbResolverService.ts
+++ b/packages/backend/src/core/activitypub/ApDbResolverService.ts
@@ -54,8 +54,8 @@ export class ApDbResolverService implements OnApplicationShutdown {
 		private cacheService: CacheService,
 		private apPersonService: ApPersonService,
 	) {
-		this.publicKeyCache = new MemoryKVCache<MiUserPublickey | null>(Infinity);
-		this.publicKeyByUserIdCache = new MemoryKVCache<MiUserPublickey | null>(Infinity);
+		this.publicKeyCache = new MemoryKVCache<MiUserPublickey | null>(1000 * 60 * 60 * 12); // 12h
+		this.publicKeyByUserIdCache = new MemoryKVCache<MiUserPublickey | null>(1000 * 60 * 60 * 12); // 12h
 	}
 
 	@bindThis
diff --git a/packages/backend/src/misc/cache.ts b/packages/backend/src/misc/cache.ts
index bba64a06ef..d968069ca3 100644
--- a/packages/backend/src/misc/cache.ts
+++ b/packages/backend/src/misc/cache.ts
@@ -7,23 +7,23 @@ import * as Redis from 'ioredis';
 import { bindThis } from '@/decorators.js';
 
 export class RedisKVCache<T> {
-	private redisClient: Redis.Redis;
-	private name: string;
-	private lifetime: number;
-	private memoryCache: MemoryKVCache<T>;
-	private fetcher: (key: string) => Promise<T>;
-	private toRedisConverter: (value: T) => string;
-	private fromRedisConverter: (value: string) => T | undefined;
+	private readonly lifetime: number;
+	private readonly memoryCache: MemoryKVCache<T>;
+	private readonly fetcher: (key: string) => Promise<T>;
+	private readonly toRedisConverter: (value: T) => string;
+	private readonly fromRedisConverter: (value: string) => T | undefined;
 
-	constructor(redisClient: RedisKVCache<T>['redisClient'], name: RedisKVCache<T>['name'], opts: {
-		lifetime: RedisKVCache<T>['lifetime'];
-		memoryCacheLifetime: number;
-		fetcher: RedisKVCache<T>['fetcher'];
-		toRedisConverter: RedisKVCache<T>['toRedisConverter'];
-		fromRedisConverter: RedisKVCache<T>['fromRedisConverter'];
-	}) {
-		this.redisClient = redisClient;
-		this.name = name;
+	constructor(
+		private redisClient: Redis.Redis,
+		private name: string,
+		opts: {
+			lifetime: RedisKVCache<T>['lifetime'];
+			memoryCacheLifetime: number;
+			fetcher: RedisKVCache<T>['fetcher'];
+			toRedisConverter: RedisKVCache<T>['toRedisConverter'];
+			fromRedisConverter: RedisKVCache<T>['fromRedisConverter'];
+		},
+	) {
 		this.lifetime = opts.lifetime;
 		this.memoryCache = new MemoryKVCache(opts.memoryCacheLifetime);
 		this.fetcher = opts.fetcher;
@@ -55,7 +55,13 @@ export class RedisKVCache<T> {
 
 		const cached = await this.redisClient.get(`kvcache:${this.name}:${key}`);
 		if (cached == null) return undefined;
-		return this.fromRedisConverter(cached);
+
+		const value = this.fromRedisConverter(cached);
+		if (value !== undefined) {
+			this.memoryCache.set(key, value);
+		}
+
+		return value;
 	}
 
 	@bindThis
@@ -77,14 +83,14 @@ export class RedisKVCache<T> {
 
 		// Cache MISS
 		const value = await this.fetcher(key);
-		this.set(key, value);
+		await this.set(key, value);
 		return value;
 	}
 
 	@bindThis
 	public async refresh(key: string) {
 		const value = await this.fetcher(key);
-		this.set(key, value);
+		await this.set(key, value);
 
 		// TODO: イベント発行して他プロセスのメモリキャッシュも更新できるようにする
 	}
@@ -101,23 +107,23 @@ export class RedisKVCache<T> {
 }
 
 export class RedisSingleCache<T> {
-	private redisClient: Redis.Redis;
-	private name: string;
-	private lifetime: number;
-	private memoryCache: MemorySingleCache<T>;
-	private fetcher: () => Promise<T>;
-	private toRedisConverter: (value: T) => string;
-	private fromRedisConverter: (value: string) => T | undefined;
+	private readonly lifetime: number;
+	private readonly memoryCache: MemorySingleCache<T>;
+	private readonly fetcher: () => Promise<T>;
+	private readonly toRedisConverter: (value: T) => string;
+	private readonly fromRedisConverter: (value: string) => T | undefined;
 
-	constructor(redisClient: RedisSingleCache<T>['redisClient'], name: RedisSingleCache<T>['name'], opts: {
-		lifetime: RedisSingleCache<T>['lifetime'];
-		memoryCacheLifetime: number;
-		fetcher: RedisSingleCache<T>['fetcher'];
-		toRedisConverter: RedisSingleCache<T>['toRedisConverter'];
-		fromRedisConverter: RedisSingleCache<T>['fromRedisConverter'];
-	}) {
-		this.redisClient = redisClient;
-		this.name = name;
+	constructor(
+		private redisClient: Redis.Redis,
+		private name: string,
+		opts: {
+			lifetime: number;
+			memoryCacheLifetime: number;
+			fetcher: RedisSingleCache<T>['fetcher'];
+			toRedisConverter: RedisSingleCache<T>['toRedisConverter'];
+			fromRedisConverter: RedisSingleCache<T>['fromRedisConverter'];
+		},
+	) {
 		this.lifetime = opts.lifetime;
 		this.memoryCache = new MemorySingleCache(opts.memoryCacheLifetime);
 		this.fetcher = opts.fetcher;
@@ -149,7 +155,13 @@ export class RedisSingleCache<T> {
 
 		const cached = await this.redisClient.get(`singlecache:${this.name}`);
 		if (cached == null) return undefined;
-		return this.fromRedisConverter(cached);
+
+		const value = this.fromRedisConverter(cached);
+		if (value !== undefined) {
+			this.memoryCache.set(value);
+		}
+
+		return value;
 	}
 
 	@bindThis
@@ -171,14 +183,14 @@ export class RedisSingleCache<T> {
 
 		// Cache MISS
 		const value = await this.fetcher();
-		this.set(value);
+		await this.set(value);
 		return value;
 	}
 
 	@bindThis
 	public async refresh() {
 		const value = await this.fetcher();
-		this.set(value);
+		await this.set(value);
 
 		// TODO: イベント発行して他プロセスのメモリキャッシュも更新できるようにする
 	}
@@ -187,22 +199,12 @@ export class RedisSingleCache<T> {
 // TODO: メモリ節約のためあまり参照されないキーを定期的に削除できるようにする？
 
 export class MemoryKVCache<T> {
-	/**
-	 * データを持つマップ
-	 * @deprecated これを直接操作するべきではない
-	 */
-	public cache: Map<string, { date: number; value: T; }>;
-	private lifetime: number;
-	private gcIntervalHandle: NodeJS.Timeout;
+	private readonly cache = new Map<string, { date: number; value: T; }>();
+	private readonly gcIntervalHandle = setInterval(() => this.gc(), 1000 * 60 * 3); // 3m
 
-	constructor(lifetime: MemoryKVCache<never>['lifetime']) {
-		this.cache = new Map();
-		this.lifetime = lifetime;
-
-		this.gcIntervalHandle = setInterval(() => {
-			this.gc();
-		}, 1000 * 60 * 3);
-	}
+	constructor(
+		private readonly lifetime: number,
+	) {}
 
 	@bindThis
 	/**
@@ -287,10 +289,14 @@ export class MemoryKVCache<T> {
 	@bindThis
 	public gc(): void {
 		const now = Date.now();
+
 		for (const [key, { date }] of this.cache.entries()) {
-			if ((now - date) > this.lifetime) {
-				this.cache.delete(key);
-			}
+			// The map is ordered from oldest to youngest.
+			// We can stop once we find an entry that's still active, because all following entries must *also* be active.
+			const age = now - date;
+			if (age < this.lifetime) break;
+
+			this.cache.delete(key);
 		}
 	}
 
@@ -298,16 +304,19 @@ export class MemoryKVCache<T> {
 	public dispose(): void {
 		clearInterval(this.gcIntervalHandle);
 	}
+
+	public get entries() {
+		return this.cache.entries();
+	}
 }
 
 export class MemorySingleCache<T> {
 	private cachedAt: number | null = null;
 	private value: T | undefined;
-	private lifetime: number;
 
-	constructor(lifetime: MemorySingleCache<never>['lifetime']) {
-		this.lifetime = lifetime;
-	}
+	constructor(
+		private lifetime: number,
+	) {}
 
 	@bindThis
 	public set(value: T): void {
diff --git a/packages/backend/src/queue/processors/DeliverProcessorService.ts b/packages/backend/src/queue/processors/DeliverProcessorService.ts
index d665945861..4076e9da90 100644
--- a/packages/backend/src/queue/processors/DeliverProcessorService.ts
+++ b/packages/backend/src/queue/processors/DeliverProcessorService.ts
@@ -45,7 +45,7 @@ export class DeliverProcessorService {
 		private queueLoggerService: QueueLoggerService,
 	) {
 		this.logger = this.queueLoggerService.logger.createSubLogger('deliver');
-		this.suspendedHostsCache = new MemorySingleCache<MiInstance[]>(1000 * 60 * 60);
+		this.suspendedHostsCache = new MemorySingleCache<MiInstance[]>(1000 * 60 * 60); // 1h
 	}
 
 	@bindThis
diff --git a/packages/backend/src/server/NodeinfoServerService.ts b/packages/backend/src/server/NodeinfoServerService.ts
index 716bb0944b..bc8d3c0411 100644
--- a/packages/backend/src/server/NodeinfoServerService.ts
+++ b/packages/backend/src/server/NodeinfoServerService.ts
@@ -135,7 +135,7 @@ export class NodeinfoServerService {
 			return document;
 		};
 
-		const cache = new MemorySingleCache<Awaited<ReturnType<typeof nodeinfo2>>>(1000 * 60 * 10);
+		const cache = new MemorySingleCache<Awaited<ReturnType<typeof nodeinfo2>>>(1000 * 60 * 10); // 10m
 
 		fastify.get(nodeinfo2_1path, async (request, reply) => {
 			const base = await cache.fetch(() => nodeinfo2(21));
diff --git a/packages/backend/src/server/api/AuthenticateService.ts b/packages/backend/src/server/api/AuthenticateService.ts
index ddef8db987..690ff2e022 100644
--- a/packages/backend/src/server/api/AuthenticateService.ts
+++ b/packages/backend/src/server/api/AuthenticateService.ts
@@ -37,7 +37,7 @@ export class AuthenticateService implements OnApplicationShutdown {
 
 		private cacheService: CacheService,
 	) {
-		this.appCache = new MemoryKVCache<MiApp>(Infinity);
+		this.appCache = new MemoryKVCache<MiApp>(1000 * 60 * 60 * 24 * 7); // 1w
 	}
 
 	@bindThis
diff --git a/packages/backend/src/server/web/UrlPreviewService.ts b/packages/backend/src/server/web/UrlPreviewService.ts
index 96038d9c1e..ef804b5bfd 100644
--- a/packages/backend/src/server/web/UrlPreviewService.ts
+++ b/packages/backend/src/server/web/UrlPreviewService.ts
@@ -38,8 +38,8 @@ export class UrlPreviewService {
 	) {
 		this.logger = this.loggerService.getLogger('url-preview');
 		this.previewCache = new RedisKVCache<SummalyResult>(this.redisClient, 'summaly', {
-			lifetime: 1000 * 86400,
-			memoryCacheLifetime: 1000 * 10 * 60,
+			lifetime: 1000 * 60 * 60 * 24, // 1d
+			memoryCacheLifetime: 1000 * 60 * 10, // 10m
 			fetcher: (key: string) => { throw new Error('the UrlPreview cache should never fetch'); },
 			toRedisConverter: (value) => JSON.stringify(value),
 			fromRedisConverter: (value) => JSON.parse(value),