{"id":1226,"date":"2021-06-25T22:55:47","date_gmt":"2021-06-25T22:55:47","guid":{"rendered":"http:\/\/feellikelearning.com\/?p=1226"},"modified":"2021-06-28T04:19:28","modified_gmt":"2021-06-28T04:19:28","slug":"algo-versioned-key-value-store","status":"publish","type":"post","link":"https:\/\/feellikelearning.com\/index.php\/2021\/06\/25\/algo-versioned-key-value-store\/","title":{"rendered":"\u7b97\u6cd5\u7ec3\u4e60\uff1a\u6709\u7248\u672c\u53f7\u7684key-value store"},"content":{"rendered":"\n<h2>\u8981\u6c42<\/h2>\n\n\n\n<p>\u5199\u4e00\u4e2akv store\uff0c\u9700\u8981\u5b9e\u73b0\u6309\u7248\u672c\u67e5\u627e\u7684method\uff0c\u7b80\u5355\u7684\u6bcf\u6b21take\u65b0snapshot\uff0c\u5c31\u628amap\u590d\u5236\u4e00\u6b21\uff0c\u653e\u5230list\u91cc\u9762\uff0c\u8fd9\u6837\u6309\u7248\u672c\u627e\u53ef\u4ee5\u5b9e\u73b0O(1)\u3002\u5982\u679c\u60f3\u7701\u7a7a\u95f4\u53ef\u4ee5\u6b21snapshot\u53ea\u5b58diff\u3002\u67e5\u7684\u65f6\u5019\u8981\u628a\u6bcf\u4e2asnapshot\u90fd\u67e5\u4e00\u6b21\uff0c\u5c31\u53d8\u6210O(num_snapshots)\u3002<\/p>\n\n\n\n<h2>Python \u5b9e\u73b0<\/h2>\n\n\n\n<pre class=\"EnlighterJSRAW\" data-enlighter-language=\"generic\" data-enlighter-theme=\"\" data-enlighter-highlight=\"\" data-enlighter-linenumbers=\"\" data-enlighter-lineoffset=\"\" data-enlighter-title=\"\" data-enlighter-group=\"\">class kvstore:\n    def __init__(self):\n        self.store = {}\n        self.snapshots = []\n        self.changed_keys = set()\n\n    def set(self, k, v):\n        self.store[k] = v\n        self.changed_keys.add(k)\n\n    def get(self, k):\n        return self.store.get(k, None) \n\n    def snapshot(self):\n        d = {}\n        for k in self.changed_keys:\n            d[k] = self.store[k]\n        self.snapshots.append(d)\n        self.changed_keys = set()\n        return len(self.snapshots) - 1\n\n    def get_from_snap(self, snap_version, key):\n        for version in range(snap_version, -1, -1):\n            if key in self.snapshots[version]:\n                return self.snapshots[version][key]\n        return None\n\nstore = kvstore()\nstore.set(\"k1\",  \"v1\")\nstore.set(\"k2\", \"v2\")\n\nassert store.get(\"k1\") == \"v1\"\n\nlast_snapshot = store.snapshot()\nassert last_snapshot == 0\nassert store.get(\"k1\") == \"v1\"\nassert store.get_from_snap(last_snapshot, \"k1\") == \"v1\"\nassert store.get_from_snap(last_snapshot, \"k2\") == \"v2\"\nassert store.get_from_snap(last_snapshot, \"k3\") == None\n\nlast_snapshot = store.snapshot()\nassert last_snapshot == 1\nassert store.get(\"k1\") == \"v1\"\nassert store.get_from_snap(last_snapshot, \"k1\") == \"v1\"\nassert store.get_from_snap(last_snapshot, \"k2\") == \"v2\"\nassert store.get_from_snap(last_snapshot, \"k3\") == None\n\nstore.set(\"k3\", \"v3\")\nstore.set(\"k2\", \"k2-1\")\nlast_snapshot = store.snapshot()\nassert last_snapshot == 2\nassert store.get(\"k1\") == \"v1\"\nassert store.get_from_snap(last_snapshot, \"k1\") == \"v1\"\nassert store.get_from_snap(last_snapshot, \"k2\") == \"k2-1\"\nassert store.get_from_snap(last_snapshot, \"k3\") == \"v3\"<\/pre>\n","protected":false},"excerpt":{"rendered":"<p>\u8981\u6c42 \u5199\u4e00\u4e2akv 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