examination/topics/networking/connection-pooling/single_choice.json

{
  "topic": "connection-pooling",
  "type": "single_choice",
  "schema_version": "1.0.0",
  "generated": "2026-09-02T21:20:00+08:00",
  "questions": [
    {
      "id": "sc-001",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "连接池",
        "基本概念"
      ],
      "question": "连接池的核心思想是什么？",
      "options": {
        "A": "每次请求都新建连接",
        "B": "预建一批连接，用时借出，用完归还而非关闭",
        "C": "关闭所有空闲连接",
        "D": "限制最大请求并发数"
      },
      "answer": "B",
      "explanation": "连接池是一批预先建好的连接集合，用时借出，用完归还而非关闭。高频场景下最简单有效的优化，避免了每次请求都要建 TCP 连接和 TLS 握手的开销。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-002",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "HTTP/1.1",
        "Keep-Alive",
        "队头阻塞"
      ],
      "question": "HTTP/1.1 的 Keep-Alive 复用存在什么限制？",
      "options": {
        "A": "不能复用连接",
        "B": "同一时刻只能有一个请求在跑（队头阻塞）",
        "C": "最多复用 3 个请求",
        "D": "需要额外付费"
      },
      "answer": "B",
      "explanation": "HTTP/1.1 的 Keep-Alive 复用虽然解决了频繁握手问题，但同一时刻只能有一个请求在跑（队头阻塞）。浏览器默认开 6 个连接来弥补。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-003",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "HTTP/2",
        "多路复用"
      ],
      "question": "HTTP/2 的多路复用如何处理多个请求？",
      "options": {
        "A": "每个请求一个 TCP 连接",
        "B": "一个 TCP 连接上并行处理多个请求/响应，通过帧编号区分",
        "C": "串行处理所有请求",
        "D": "使用 UDP 协议"
      },
      "answer": "B",
      "explanation": "HTTP/2 的多路复用在一个 TCP 连接上同时跑多个请求/响应，通过帧编号区分。不再需要多个 TCP 连接来并行，一根连接全部搞定。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-004",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "连接池",
        "配置"
      ],
      "question": "连接池最大连接数设得过大可能导致什么问题？",
      "options": {
        "A": "请求处理速度变慢",
        "B": "内存和文件描述符浪费",
        "C": "连接加密失败",
        "D": "DNS 解析变慢"
      },
      "answer": "B",
      "explanation": "连接池最大连接数过大，每个连接都占内存和 fd，导致资源浪费。应该根据服务端能承受的并发数和实际需求合理配置。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-005",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "僵尸连接",
        "健康检查"
      ],
      "question": "连接池中的僵尸连接是什么？",
      "options": {
        "A": "正在使用的连接",
        "B": "服务器端已关闭但客户端不知道，下次复用时发现连接已死",
        "C": "加密失败的连接",
        "D": "超时的连接"
      },
      "answer": "B",
      "explanation": "僵尸连接是指服务器端已经关闭了连接，但客户端不知道，下次复用时发现连接已死。解决方案：开启连接健康检查、设置合理的空闲超时、使用 TCP keepalive。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-006",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "连接池",
        "Python"
      ],
      "question": "Python requests 库中，pool_maxsize 参数控制什么？",
      "options": {
        "A": "最大请求数",
        "B": "每个池子最多保持的连接数",
        "C": "请求超时时间",
        "D": "重试次数"
      },
      "answer": "B",
      "explanation": "pool_maxsize 控制每个池子最多保持的连接数。pool_connections 是连接到不同目标服务器的池子数。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-007",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "连接池",
        "HTTP/2"
      ],
      "question": "HTTP/2 的多路复用还需要连接池吗？",
      "options": {
        "A": "完全不需要",
        "B": "仍然需要，连接池提供容错和负载均衡能力",
        "C": "只需要 1 个连接",
        "D": "连接池会干扰多路复用"
      },
      "answer": "B",
      "explanation": "连接池仍然有用。HTTP/2 解决了单个连接上的并行问题，但连接池提供了容错（一个连接挂了可以切到另一个）和负载均衡（多连接分散压力）的能力。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-008",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "连接池",
        "Go"
      ],
      "question": "Go 的 http.Transport 中 MaxIdleConnsPerHost 参数控制什么？",
      "options": {
        "A": "最大空闲连接总数",
        "B": "每个主机最多保留的空闲连接数",
        "C": "连接超时时间",
        "D": "最大并发请求数"
      },
      "answer": "B",
      "explanation": "MaxIdleConnsPerHost 控制每个主机最多保留的空闲连接数。MaxIdleConns 是最大空闲连接总数，IdleConnTimeout 是空闲连接超时时间。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-009",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "连接池",
        "延迟"
      ],
      "question": "连接池打满时会发生什么？",
      "options": {
        "A": "自动扩容",
        "B": "新请求排队等连接，延迟飙升",
        "C": "直接拒绝请求",
        "D": "自动建立新连接"
      },
      "answer": "B",
      "explanation": "连接池打满时，新请求需要排队等连接归还，导致延迟飙升。解决方案：合理调大池子，或用 HTTP/2 多路复用减少对连接数的需求。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-010",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "连接池",
        "Java"
      ],
      "question": "Java Apache HttpClient 中 setDefaultMaxPerRoute(20) 的含义是？",
      "options": {
        "A": "总连接池大小为 20",
        "B": "每个目标服务器最多 20 个连接",
        "C": "最大空闲连接为 20",
        "D": "连接超时 20 秒"
      },
      "answer": "B",
      "explanation": "setDefaultMaxPerRoute(20) 表示每个目标服务器（路由）最多 20 个连接。setMaxTotal(200) 才是总连接池大小。",
      "source": null,
      "related": []
    }
  ]
}