feat: add 50 backend interview questions and answers
Generated comprehensive interview preparation materials covering: - Distributed systems (transactions, locks, ID generation, consistency) - Database (indexing, sharding, replication, transactions) - Caching (Redis, cache problems, distributed lock) - Message queues (RocketMQ, Kafka) - Concurrency (ThreadLocal, ConcurrentHashMap, thread pools) - JVM (GC, memory, tuning) - System design (seckill, short URL, IM, feed, LBS) - Algorithms (B+ tree, LRU, Red-Black tree, Skip list, Timing wheel) - Network (TCP/IP, HTTP/HTTPS) - Security (encryption, SQL injection, XSS) - Performance tuning - Design patterns - Microservices (Spring Boot, Gateway, Service Mesh) - Container orchestration (Kubernetes, Docker) - CI/CD, observability Each file includes: - Detailed questions - Comprehensive answers - Code examples - Real project experience - Alibaba P7 level requirements Generated with [Claude Code](https://claude.com/claude-code) via [Happy](https://happy.engineering) Co-Authored-By: Claude <noreply@anthropic.com> Co-Authored-By: Happy <yesreply@happy.engineering>
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yasinshaw
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questions/redis-data-structure.md
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questions/redis-data-structure.md
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# Redis 数据结构
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## 问题
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1. Redis 有哪些数据结构？底层实现是什么？
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2. String 类型的应用场景？
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3. Hash 和 String 的区别？
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4. List 的应用场景？
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5. Set 和 ZSet 的区别？
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6. Bitmap、HyperLogLog、GEO 的应用？
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---
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## 标准答案
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### 1. Redis 数据类型
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| 类型 | 底层实现 | 应用场景 |
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|------|---------|----------|
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| **String** | SDS | 缓存、计数器、分布式锁 |
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| **Hash** | 压缩列表/哈希表 | 对象存储、购物车 |
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| **List** | 双向链表/压缩列表 | 消息队列、最新列表 |
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| **Set** | 哈希表/整数集合 | 标签、共同关注 |
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| **ZSet** | 跳表/哈希表 | 排行榜、延时队列 |
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| **Bitmap** | String（位操作） | 签到、在线用户 |
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| **HyperLogLog** | String（基数统计） | UV 统计 |
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| **GEO** | ZSet（经纬度编码） | 附近的人 |
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---
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### 2. String（SDS - Simple Dynamic String）
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**结构**：
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```c
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struct sdshdr {
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int len; // 已使用长度
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int free; // 剩余空间
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char buf[]; // 字节数组
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};
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```
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**优势**：
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- O(1) 获取长度
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- 防止缓冲区溢出
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- 减少内存分配次数
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**应用**：
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```bash
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# 缓存
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SET user:1001 '{"id":1001,"name":"Alice"}'
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GET user:1001
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# 计数器
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INCR view_count:1001
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DECR stock:1001
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# 分布式锁
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SET lock:order:1001 "uuid" NX PX 30000
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```
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---
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### 3. Hash
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**结构**：
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```bash
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HSET user:1001 name "Alice" age 25 email "alice@example.com"
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HGET user:1001 name
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HGETALL user:1001
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```
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**底层**：
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- 字段少（< 512）：压缩列表（ziplist）
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- 字段多（≥ 512）：哈希表（hashtable）
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**应用**：
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```java
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// 对象存储（推荐 Hash，而非 String）
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redisTemplate.opsForHash().putAll("user:1001", Map.of(
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"name", "Alice",
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"age", "25"
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));
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// 购物车
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redisTemplate.opsForHash().put("cart:1001", "product:1001", "2");
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```
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---
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### 4. List
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**结构**：
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```bash
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LPUSH list:msgs "msg1" "msg2" "msg3" # 左侧插入
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RPOP list:msgs # 右侧弹出
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```
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**底层**：
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- 元素少（< 512）：压缩列表（ziplist）
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- 元素多（≥ 512）：双向链表（linkedlist）
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- Redis 3.2+：quicklist（ziplist + linkedlist）
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**应用**：
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```bash
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# 消息队列
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LPUSH queue:email '{"to":"alice@example.com","subject":"Hello"}'
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RPOP queue:email
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# 最新列表
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LPUSH timeline:1001 "post1" "post2"
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LRANGE timeline:1001 0 9 # 最新 10 条
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```
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---
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### 5. Set vs ZSet
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**Set（无序集合）**：
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```bash
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SADD tags:article:1001 "java" "redis" "mysql"
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SMEMBERS tags:article:1001
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SISMEMBER tags:article:1001 "java"
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SINTER tags:user:1001 tags:article:1001 # 交集
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```
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**底层**：
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- 元素少（< 512）：整数集合（intset）
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- 元素多（≥ 512）：哈希表（hashtable）
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---
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**ZSet（有序集合）**：
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```bash
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ZADD rank:score 100 "player1" 200 "player2" 150 "player3"
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ZREVRANGE rank:score 0 9 WITHSCORES # Top 10
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ZRANK rank:score "player1" # 排名
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ZSCORE rank:score "player1" # 分数
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```
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**底层**：
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- 元素少（< 128）：压缩列表（ziplist）
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- 元素多（≥ 128）：跳表（skiplist） + 哈希表（hashtable）
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---
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### 6. Bitmap
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**原理**：用 bit 位表示状态（0 或 1）
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```bash
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# 签到
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SETBIT sign:2024:02:28:1001 0 1 # 用户 1001 在第 0 天签到
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SETBIT sign:2024:02:28:1001 4 1 # 用户 1001 在第 4 天签到
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# 统计签到天数
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BITCOUNT sign:2024:02:28:1001
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# 用户 1001 和 1002 共同签到的天数
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BITOP AND result sign:2024:02:28:1001 sign:2024:02:28:1002
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BITCOUNT result
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```
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---
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### 7. HyperLogLog
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**用途**：基数统计（不重复元素个数）
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**优点**：内存占用极小（12 KB）
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```bash
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PFADD uv:2024:02:28 user:1001 user:1002 user:1003
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PFCOUNT uv:2024:02:28 # 3
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# 合并多个 HyperLogLog
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PFMERGE uv:2024:02:01-28 uv:2024:02:01 uv:2024:02:02 ...
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```
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**误差率**：< 1%
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---
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### 8. GEO（地理位置）
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```bash
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# 添加位置
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GEOADD locations:users 116.404 39.915 "user:1001" # 北京
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# 查找附近的人（5 km 内）
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GEORADIUS locations:users 116.404 39.915 5 km
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# 计算距离
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GEODIST locations:users user:1001 user:1002
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```
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**底层**：ZSet（经纬度编码为 score）
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---
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### 9. 阿里 P7 加分项
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**深度理解**：
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- 理解 SDS 和 C 字符串的区别
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- 理解跳表的实现原理
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- 理解压缩列表的优缺点
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**实战经验**：
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- 有选择合适数据类型的经验
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- 有大数据量下的优化经验
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- 有 Redis 内存优化的经验
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**架构能力**：
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- 能设计基于 Redis 的业务方案
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- 能设计 Redis 集群方案
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- 能设计 Redis 监控体系
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