""" Ch10 配套代码 1 / 3 —— CRC16 算法 + Slot 计算 + HashTag 演示 演示： 1. 自己实现 Redis 用的 CRC16-CCITT（XMODEM 变体）算法 2. 对若干 key 计算 slot = CRC16(key) % 16384 3. HashTag {tag}:xxx 强制同槽 —— 业务关联 key 必落同节点 4. HashTag 解析的边界 case（{}、{a}{b}、嵌套） 无需连接 Redis Server，纯算法演示。 """ from typing import Optional # ────────────────────────────────────────────────────────────── # Redis 集群使用的 CRC16-CCITT (XMODEM) 算法 # 多项式：0x1021；初始值：0x0000；不反转 # 这张 256 项的查找表是 Redis 源码 src/crc16.c 里的原表 # ────────────────────────────────────────────────────────────── CRC16TAB = [ 0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50A5, 0x60C6, 0x70E7, 0x8108, 0x9129, 0xA14A, 0xB16B, 0xC18C, 0xD1AD, 0xE1CE, 0xF1EF, 0x1231, 0x0210, 0x3273, 0x2252, 0x52B5, 0x4294, 0x72F7, 0x62D6, 0x9339, 0x8318, 0xB37B, 0xA35A, 0xD3BD, 0xC39C, 0xF3FF, 0xE3DE, 0x2462, 0x3443, 0x0420, 0x1401, 0x64E6, 0x74C7, 0x44A4, 0x5485, 0xA56A, 0xB54B, 0x8528, 0x9509, 0xE5EE, 0xF5CF, 0xC5AC, 0xD58D, 0x3653, 0x2672, 0x1611, 0x0630, 0x76D7, 0x66F6, 0x5695, 0x46B4, 0xB75B, 0xA77A, 0x9719, 0x8738, 0xF7DF, 0xE7FE, 0xD79D, 0xC7BC, 0x48C4, 0x58E5, 0x6886, 0x78A7, 0x0840, 0x1861, 0x2802, 0x3823, 0xC9CC, 0xD9ED, 0xE98E, 0xF9AF, 0x8948, 0x9969, 0xA90A, 0xB92B, 0x5AF5, 0x4AD4, 0x7AB7, 0x6A96, 0x1A71, 0x0A50, 0x3A33, 0x2A12, 0xDBFD, 0xCBDC, 0xFBBF, 0xEB9E, 0x9B79, 0x8B58, 0xBB3B, 0xAB1A, 0x6CA6, 0x7C87, 0x4CE4, 0x5CC5, 0x2C22, 0x3C03, 0x0C60, 0x1C41, 0xEDAE, 0xFD8F, 0xCDEC, 0xDDCD, 0xAD2A, 0xBD0B, 0x8D68, 0x9D49, 0x7E97, 0x6EB6, 0x5ED5, 0x4EF4, 0x3E13, 0x2E32, 0x1E51, 0x0E70, 0xFF9F, 0xEFBE, 0xDFDD, 0xCFFC, 0xBF1B, 0xAF3A, 0x9F59, 0x8F78, 0x9188, 0x81A9, 0xB1CA, 0xA1EB, 0xD10C, 0xC12D, 0xF14E, 0xE16F, 0x1080, 0x00A1, 0x30C2, 0x20E3, 0x5004, 0x4025, 0x7046, 0x6067, 0x83B9, 0x9398, 0xA3FB, 0xB3DA, 0xC33D, 0xD31C, 0xE37F, 0xF35E, 0x02B1, 0x1290, 0x22F3, 0x32D2, 0x4235, 0x5214, 0x6277, 0x7256, 0xB5EA, 0xA5CB, 0x95A8, 0x8589, 0xF56E, 0xE54F, 0xD52C, 0xC50D, 0x34E2, 0x24C3, 0x14A0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405, 0xA7DB, 0xB7FA, 0x8799, 0x97B8, 0xE75F, 0xF77E, 0xC71D, 0xD73C, 0x26D3, 0x36F2, 0x0691, 0x16B0, 0x6657, 0x7676, 0x4615, 0x5634, 0xD94C, 0xC96D, 0xF90E, 0xE92F, 0x99C8, 0x89E9, 0xB98A, 0xA9AB, 0x5844, 0x4865, 0x7806, 0x6827, 0x18C0, 0x08E1, 0x3882, 0x28A3, 0xCB7D, 0xDB5C, 0xEB3F, 0xFB1E, 0x8BF9, 0x9BD8, 0xABBB, 0xBB9A, 0x4A75, 0x5A54, 0x6A37, 0x7A16, 0x0AF1, 0x1AD0, 0x2AB3, 0x3A92, 0xFD2E, 0xED0F, 0xDD6C, 0xCD4D, 0xBDAA, 0xAD8B, 0x9DE8, 0x8DC9, 0x7C26, 0x6C07, 0x5C64, 0x4C45, 0x3CA2, 0x2C83, 0x1CE0, 0x0CC1, 0xEF1F, 0xFF3E, 0xCF5D, 0xDF7C, 0xAF9B, 0xBFBA, 0x8FD9, 0x9FF8, 0x6E17, 0x7E36, 0x4E55, 0x5E74, 0x2E93, 0x3EB2, 0x0ED1, 0x1EF0, ] CLUSTER_SLOTS = 16384 def crc16(data: bytes) -> int: """Redis 用的 CRC16-CCITT (XMODEM) 算法""" crc = 0x0000 for b in data: crc = ((crc << 8) & 0xFFFF) ^ CRC16TAB[((crc >> 8) ^ b) & 0xFF] return crc def extract_hashtag(key: str) -> Optional[str]: """提取 HashTag：第一对非空 {...} 之间的内容 若无有效 HashTag，返回 None（用整个 key 计算）""" start = key.find("{") if start == -1: return None end = key.find("}", start + 1) if end == -1 or end == start + 1: # } 不存在 或 {} 中间为空 return None return key[start + 1:end] def key_slot(key: str) -> int: """模拟 Redis 的 keyHashSlot：先抽 HashTag，再 CRC16 % 16384""" tag = extract_hashtag(key) target = tag if tag is not None else key return crc16(target.encode("utf-8")) % CLUSTER_SLOTS def section(title: str) -> None: print("\n" + "=" * 64) print(title) print("=" * 64) def demo_basic_slot() -> None: section("Demo 1: 普通 key 的 slot 计算") keys = ["user:1001", "user:1002", "user:1003", "order:8888", "product:42", "session:abc", "foo", "bar", "baz", "hello world"] for k in keys: s = key_slot(k) print(f" {k:25} → slot = {s:5}") def demo_hashtag() -> None: section("Demo 2: HashTag 强制同槽") keys = [ "{user:1001}:profile", "{user:1001}:cart", "{user:1001}:orders", "{user:1001}:wishlist", ] print(" 同一 user 的 4 个相关 key（带 HashTag {user:1001}）：") for k in keys: s = key_slot(k) print(f" {k:35} → slot = {s:5}") print(" ✅ 全部落在同一 slot —— 同节点 → 支持事务/MGET/Lua") print("\n 对比：不带 HashTag 时 4 个 key 各自飘散：") for k in ["user:1001:profile", "user:1001:cart", "user:1001:orders", "user:1001:wishlist"]: s = key_slot(k) print(f" {k:35} → slot = {s:5}") def demo_hashtag_edge_cases() -> None: section("Demo 3: HashTag 解析的边界 case") cases = [ ("{abc}:def", "abc", "正常 HashTag"), ("abc{def}ghi", "def", "中间含 HashTag"), ("{}foo", "{}foo", "{} 为空 → 无效，回退整个 key"), ("{a}{b}", "a", "多对花括号 → 只看第一对"), ("{a{b}c}", "a{b", "嵌套 → 第一个 } 截断"), ("abc", "abc", "无花括号"), ("{abc", "{abc", "缺右括号 → 无效"), ("abc}", "abc}", "缺左括号 → 无效"), ] print(f" {'输入 key':<15} {'实际参与 hash 的内容':<20} {'slot':>6} 说明") print(" " + "─" * 70) for k, expected, desc in cases: s = key_slot(k) actual = extract_hashtag(k) or k ok = "✓" if actual == expected else "✗" print(f" {k:<15} {actual:<20} {s:>6} {desc} [{ok}]") def demo_distribution() -> None: section("Demo 4: 1 万个随机 key 在 3 节点上的分布均衡度") # 3 个节点平分 16384 槽 ranges = [(0, 5460), (5461, 10922), (10923, 16383)] counters = [0, 0, 0] for i in range(10000): k = f"key:{i}" s = key_slot(k) for idx, (lo, hi) in enumerate(ranges): if lo <= s <= hi: counters[idx] += 1 break total = sum(counters) print(f" {'节点':<12} {'slot 范围':<15} {'key 数':>8} 占比") print(" " + "─" * 50) for i, ((lo, hi), c) in enumerate(zip(ranges, counters)): pct = c / total * 100 bar = "█" * int(pct / 2) print(f" Node-{i+1:<7} {lo:5}~{hi:<8} {c:>8} {pct:5.2f}% {bar}") print(" 💡 CRC16 + 16384 槽 → 分布相当均匀（理想 33.33%）") if __name__ == "__main__": demo_basic_slot() demo_hashtag() demo_hashtag_edge_cases() demo_distribution()