{
  "topic": "http-connection-cost",
  "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": [
        "TCP",
        "内存",
        "内核"
      ],
      "question": "操作系统为每个 TCP 连接分配的内核内存大约是多少？",
      "options": {
        "A": "300-1000 KB",
        "B": "3-10 KB",
        "C": "1-2 KB",
        "D": "50-100 KB"
      },
      "answer": "B",
      "explanation": "操作系统为每个 TCP 连接分配的内核内存大约是 3-10 KB，包括发送/接收缓冲区和 TCP 控制块。50-100 KB 是 HTTPS 场景下 TLS 会话的额外消耗。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-002",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "线程模型",
        "协程模型"
      ],
      "question": "传统线程模型（Java BIO）每连接的内存消耗大约是多少？",
      "options": {
        "A": "约 4 KB",
        "B": "约 10 KB",
        "C": "约 1 MB",
        "D": "约 10 MB"
      },
      "answer": "C",
      "explanation": "传统线程模型每连接约 1 MB（主要是线程栈），协程模型（Go/async）仅需约 4 KB，异步事件驱动（Nginx）约 2 KB。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-003",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "百万并发",
        "内存"
      ],
      "question": "百万并发场景下，使用传统线程模型需要多少内存？",
      "options": {
        "A": "约 10 GB",
        "B": "约 50 GB",
        "C": "约 1 TB",
        "D": "约 4 GB"
      },
      "answer": "C",
      "explanation": "传统线程模型每连接约 1 MB，百万并发需要约 1 TB 内存，这在物理上不可行。协程模型约 4 GB 是可行的。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-004",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "TCP",
        "端口"
      ],
      "question": "客户端临时端口的理论上限是多少？",
      "options": {
        "A": "1024",
        "B": "32768",
        "C": "65535",
        "D": "1048576"
      },
      "answer": "C",
      "explanation": "客户端端口是 16 位整数，理论上限 65535。每个 TCP 连接需要一个唯一的四元组（源IP:源端口:目标IP:目标端口）。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-005",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "Go",
        "goroutine",
        "协程"
      ],
      "question": "Go goroutine 的初始栈大小是多少？",
      "options": {
        "A": "1 KB",
        "B": "2 KB",
        "C": "4 KB",
        "D": "8 KB"
      },
      "answer": "B",
      "explanation": "Go goroutine 初始栈大小为 2 KB（可动态增长到 1 GB），Java 线程默认栈大小为 1 MB。相同内存下 Go 能创建的并发单元数量是 Java 的约 500 倍。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-006",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "TLS",
        "HTTPS",
        "内存"
      ],
      "question": "HTTPS 场景下 TLS 会话缓存每个连接额外消耗多少内存？",
      "options": {
        "A": "3-10 KB",
        "B": "50-100 KB",
        "C": "200-500 KB",
        "D": "1-2 MB"
      },
      "answer": "B",
      "explanation": "HTTPS 场景下 TLS 会话缓存每个连接额外消耗 50-100 KB 内存，百万并发下可能吃掉 50 GB 内存。因此考虑在 CDN 边缘终止 TLS。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-007",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "文件描述符",
        "ulimit"
      ],
      "question": "每个 TCP 连接占多少个文件描述符？",
      "options": {
        "A": "0 个",
        "B": "1 个",
        "C": "2 个",
        "D": "4 个"
      },
      "answer": "B",
      "explanation": "每个 TCP 连接占 1 个文件描述符（fd），受系统 ulimit 限制。百万并发需要调大 ulimit 到至少 1048576。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-008",
      "type": "single_choice",
      "difficulty": 4,
      "tags": [
        "异步模型",
        "Nginx",
        "事件驱动"
      ],
      "question": "异步事件驱动模型（如 Nginx）每连接的内存消耗大约是多少？",
      "options": {
        "A": "约 1 MB",
        "B": "约 10 KB",
        "C": "约 4 KB",
        "D": "约 2 KB"
      },
      "answer": "D",
      "explanation": "异步事件驱动模型（Nginx）每连接约 2 KB，几乎不占位置。这是最高效的连接模型，但编程复杂度最高。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-009",
      "type": "single_choice",
      "difficulty": 3,
      "tags": [
        "Epoll",
        "Kqueue",
        "IO多路复用"
      ],
      "question": "撑住百万并发的关键手段中，Epoll/Kqueue 的作用是什么？",
      "options": {
        "A": "为每个连接开一个线程",
        "B": "不为每个连接开线程，一个线程监控百万 fd",
        "C": "加密所有连接",
        "D": "压缩数据传输"
      },
      "answer": "B",
      "explanation": "Epoll/Kqueue 是 IO 多路复用机制，不为每个连接开线程，一个线程就能监控百万文件描述符，是撑住百万并发的关键手段之一。",
      "source": null,
      "related": []
    },
    {
      "id": "sc-010",
      "type": "single_choice",
      "difficulty": 2,
      "tags": [
        "TCP",
        "资源"
      ],
      "question": "TCP 连接的四元组中不包括以下哪项？",
      "options": {
        "A": "源 IP",
        "B": "源端口",
        "C": "协议号",
        "D": "目标端口"
      },
      "answer": "C",
      "explanation": "TCP 连接的四元组是：源 IP、源端口、目标 IP、目标端口。协议号（TCP=6）是固定的，不属于四元组。",
      "source": null,
      "related": []
    }
  ]
}