diff --git a/CHANGELOG.md b/CHANGELOG.md
index c3d6dcf535..7a8873ba0d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,8 @@
 - Fix: 無制限にストリーミングのチャンネルに接続できる問題を修正
 - Fix: ベースロールのポリシーを変更した際にモデログに記録されないのを修正  
   (Cherry-picked from https://github.com/MisskeyIO/misskey/pull/700)
+- Fix: Prevent memory leak from memory caches (#14310)
+- Fix: More reliable memory cache eviction (#14311)
 
 ## 2024.7.0
 
diff --git a/packages/backend/src/core/AvatarDecorationService.ts b/packages/backend/src/core/AvatarDecorationService.ts
index 8b54bbe012..4efd6122b1 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 7e11b9cdca..5db3c5b980 100644
--- a/packages/backend/src/core/CustomEmojiService.ts
+++ b/packages/backend/src/core/CustomEmojiService.ts
@@ -24,7 +24,7 @@ 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(
@@ -40,7 +40,7 @@ export class CustomEmojiService implements OnApplicationShutdown {
 		private moderationLogService: ModerationLogService,
 		private globalEventService: GlobalEventService,
 	) {
-		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
@@ -334,7 +334,7 @@ export class CustomEmojiService implements OnApplicationShutdown {
 			host,
 		})) ?? 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）
@@ -361,7 +361,7 @@ 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} ${emoji.host}`) == null);
 		const emojisQuery: any[] = [];
 		const hosts = new Set(notCachedEmojis.map(e => e.host));
 		for (const host of hosts) {
@@ -376,7 +376,7 @@ export class CustomEmojiService implements OnApplicationShutdown {
 			select: ['name', 'host', 'originalUrl', 'publicUrl'],
 		}) : [];
 		for (const emoji of _emojis) {
-			this.cache.set(`${emoji.name} ${emoji.host}`, emoji);
+			this.emojisCache.set(`${emoji.name} ${emoji.host}`, emoji);
 		}
 	}
 
@@ -401,7 +401,7 @@ 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 8dd3d64f5b..db32114346 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 7966774673..0210012a03 100644
--- a/packages/backend/src/core/RoleService.ts
+++ b/packages/backend/src/core/RoleService.ts
@@ -127,10 +127,8 @@ 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 f6b70ead44..4192e8659a 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..f9692ce5d5 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
@@ -66,6 +72,10 @@ export class RedisKVCache<T> {
 
 	/**
 	 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
+	 * This awaits the call to Redis to ensure that the write succeeded, which is important for a few reasons:
+	 *   * Other code uses this to synchronize changes between worker processes. A failed write can internally de-sync the cluster.
+	 *   * Without an `await`, consecutive calls could race. An unlucky race could result in the older write overwriting the newer value.
+	 *   * Not awaiting here makes the entire cache non-consistent. The prevents many possible uses.
 	 */
 	@bindThis
 	public async fetch(key: string): Promise<T> {
@@ -77,14 +87,14 @@ 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 +111,23 @@ 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 +159,13 @@ 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
@@ -160,6 +176,10 @@ export class RedisSingleCache<T> {
 
 	/**
 	 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
+	 * This awaits the call to Redis to ensure that the write succeeded, which is important for a few reasons:
+	 *   * Other code uses this to synchronize changes between worker processes. A failed write can internally de-sync the cluster.
+	 *   * Without an `await`, consecutive calls could race. An unlucky race could result in the older write overwriting the newer value.
+	 *   * Not awaiting here makes the entire cache non-consistent. The prevents many possible uses.
 	 */
 	@bindThis
 	public async fetch(): Promise<T> {
@@ -171,14 +191,14 @@ 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 +207,12 @@ 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 +297,14 @@ 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 +312,19 @@ 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 cc18997fdc..9a641007ee 100644
--- a/packages/backend/src/server/NodeinfoServerService.ts
+++ b/packages/backend/src/server/NodeinfoServerService.ts
@@ -134,7 +134,7 @@ 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