{
  "topic": "cache-three-problems",
  "type": "fill_blank",
  "schema_version": "1.0.0",
  "generated": "2026-09-05T00:00:00+08:00",
  "questions": [
    {
      "id": "fb-001",
      "type": "fill_blank",
      "difficulty": 1,
      "tags": [
        "缓存穿透"
      ],
      "question": "缓存穿透是指查询一个数据库中也______的数据，导致每次请求都直达数据库。",
      "answer": [
        "不存在"
      ],
      "answer_rule": "any",
      "explanation": "缓存穿透的本质是查询的 key 在数据库中也【不存在】，缓存查不到、写不回，因此每次请求都要穿透到 DB。",
      "source": null,
      "related": []
    },
    {
      "id": "fb-002",
      "type": "fill_blank",
      "difficulty": 1,
      "tags": [
        "缓存击穿"
      ],
      "question": "缓存击穿是______个热点 key 缓存【刚好过期】，大量请求同时打数据库，特点是单 key、高并发。",
      "answer": [
        "一",
        "单",
        "1",
        "一个"
      ],
      "answer_rule": "any",
      "explanation": "击穿针对的是「单个特别热门的 key」刚过期，与穿透（不存在）和雪崩（成批）都不同，关键词是「单」。",
      "source": null,
      "related": []
    },
    {
      "id": "fb-003",
      "type": "fill_blank",
      "difficulty": 1,
      "tags": [
        "缓存雪崩"
      ],
      "question": "缓存雪崩指______大批 key 在同一时刻集体失效，或整台缓存服务宕机，瞬时请求全部穿透到数据库。",
      "answer": [
        "一批",
        "成批",
        "多个",
        "很多",
        "大量"
      ],
      "answer_rule": "any",
      "explanation": "雪崩的关键词是「多 key / 成批 / 集体失效」，与击穿的单 key 形成对比。",
      "source": null,
      "related": []
    },
    {
      "id": "fb-004",
      "type": "fill_blank",
      "difficulty": 2,
      "tags": [
        "缓存穿透",
        "缓存空对象"
      ],
      "question": "用「缓存空对象」防穿透：DB 查不到时也缓存一个 null，并设置______（如 5 分钟）的 TTL。",
      "answer": [
        "极短",
        "很短",
        "较短",
        "短"
      ],
      "answer_rule": "any",
      "explanation": "空值必须用极短 TTL，防止大量不同空 key 长期占用内存导致缓存爆掉。",
      "source": null,
      "related": []
    },
    {
      "id": "fb-005",
      "type": "fill_blank",
      "difficulty": 2,
      "tags": [
        "缓存穿透",
        "布隆过滤器"
      ],
      "question": "布隆过滤器判断「不存在」时数据一定不存在（无______），判断「存在」时却可能存在（有______），且不支持删除。",
      "answer": [
        "假阴性",
        "假阳性"
      ],
      "answer_rule": "ordered",
      "explanation": "布隆过滤器无假阴性（说不存在就一定不存在），有假阳性（说存在却可能不存在）。空按题目顺序填写「假阴性、假阳性」，因此 answer_rule 用 ordered。",
      "source": null,
      "related": []
    },
    {
      "id": "fb-006",
      "type": "fill_blank",
      "difficulty": 2,
      "tags": [
        "缓存击穿",
        "互斥锁",
        "SETNX"
      ],
      "question": "用互斥锁解决击穿时，常用 Redis 的______命令实现分布式锁，保证同时只有一个请求回源数据库并回填缓存。",
      "answer": [
        "SETNX",
        "setnx",
        "SET NX",
        "SETNXEX"
      ],
      "answer_rule": "any",
      "explanation": "SETNX（SET if Not eXists）是 Redis 实现分布式锁最常用的命令：抢到锁的请求才回源，其余等待或降级。",
      "source": null,
      "related": []
    },
    {
      "id": "fb-007",
      "type": "fill_blank",
      "difficulty": 3,
      "tags": [
        "缓存击穿",
        "逻辑过期"
      ],
      "question": "「逻辑过期」方案不真正删除缓存，到期后由______异步线程去更新，保证数据持续可用。",
      "answer": [
        "后台",
        "异步",
        "后台异步",
        "独立"
      ],
      "answer_rule": "any",
      "explanation": "逻辑过期由后台异步线程在后台刷新缓存，从而挡住所拦截的并发瞬时冲击，保证数据持续可用。",
      "source": null,
      "related": []
    },
    {
      "id": "fb-008",
      "type": "fill_blank",
      "difficulty": 3,
      "tags": [
        "缓存雪崩",
        "TTL加随机"
      ],
      "question": "给缓存 key 的过期时间加______值（如 60+random(0~300) 秒），可把到期时刻打散，避免一批 key 同时失效。",
      "answer": [
        "随机",
        "随机偏差",
        "随机数",
        "随机量"
      ],
      "answer_rule": "any",
      "explanation": "TTL 加随机值把各 key 的到期时间分散开，防止同一时刻集体失效的雪崩。",
      "source": null,
      "related": []
    },
    {
      "id": "fb-009",
      "type": "fill_blank",
      "difficulty": 4,
      "tags": [
        "多级缓存",
        "缓存雪崩"
      ],
      "question": "多级缓存的访问顺序是：本地进程内缓存 → ______ → DB，层层兜底防雪崩。",
      "answer": [
        "Redis",
        "分布式缓存",
        "缓存层",
        "分布式缓存层"
      ],
      "answer_rule": "any",
      "explanation": "典型多级缓存顺序为本地缓存（进程内）→ Redis（分布式缓存层）→ DB，逐层兜底，减小某层失效带来的冲击。",
      "source": null,
      "related": []
    },
    {
      "id": "fb-010",
      "type": "fill_blank",
      "difficulty": 4,
      "tags": [
        "Redis高可用",
        "缓存雪崩"
      ],
      "question": "为避免整台缓存服务宕机引发雪崩，可采用______（主从+哨兵）或集群方案保证缓存层高可用。",
      "answer": [
        "主从",
        "主从复制",
        "哨兵",
        "主从哨兵",
        "高可用架构"
      ],
      "answer_rule": "any",
      "explanation": "Redis 高可用通常由主从复制 + 哨兵（故障自动切换）+ 集群（分片）组成，避免整机宕机导致缓存雪崩。",
      "source": null,
      "related": []
    }
  ]
}