Node.js Express应用中高效内存缓存策略与实践

let data = null; // 全局变量用于存储缓存数据

// 每30秒刷新一次数据
setInterval(async () => {
    try {
        data = await collection.find({
            data: { $ne: 'old'},
            $or: [
                { "currentRanks.minuteTokenRank": {$lt: 51} },
                { "currentRanks.fiveMinuteTokenRank": {$lt: 51} },
                { "currentRanks.fifteenMinuteTokenRank": {$lt: 51} },
                { "currentRanks.thirtyMinuteTokenRank": {$lt: 51} },
                { "currentRanks.hourlyTokenRank": {$lt: 51} },
                { "currentRanks.dailyTokenRank": {$lt: 51} },
                { "currentRanks.weeklyTokenRank": {$lt: 51} }
            ]
        }).lean();
    } catch (error) {
      console.error("Error refreshing data:", error);
      // 捕获错误，避免中断interval
    }
}, 30000);

export async function main(req, reply) {
    try {
        let datares = data; // 从缓存中获取数据
        reply.status(200).send(datares);
        // datares = null; // 此行代码无效，因为datares是局部变量
    } catch (err) {
        reply.status(500).send({ message: err.message });
        console.log('err', err.message);
    }
}

// cacheService.js
const { MongoClient } = require('mongodb'); // 假设已配置MongoDB连接
const MONGO_URI = 'mongodb://localhost:27017/mydb'; // 你的MongoDB连接字符串
const DB_NAME = 'mydb';
let collection; // MongoDB集合实例

let cachedData = null;
let lastRefreshTime = 0;
const CACHE_REFRESH_INTERVAL = 30 * 1000; // 30秒

// 连接MongoDB的函数
async function connectToMongo() {
    if (!collection) {
        try {
            const client = await MongoClient.connect(MONGO_URI, { useNewUrlParser: true, useUnifiedTopology: true });
            const db = client.db(DB_NAME);
            collection = db.collection('mycollection'); // 替换为你的集合名称
            console.log("MongoDB connected successfully for cache service.");
        } catch (error) {
            console.error("Failed to connect to MongoDB for cache service:", error);
            process.exit(1); // 连接失败则退出应用
        }
    }
}

// 从数据库获取数据的核心逻辑
async function fetchDataFromDB() {
    if (!collection) {
        await connectToMongo(); // 确保MongoDB已连接
    }
    try {
        const data = await collection.find({
            data: { $ne: 'old'},
            $or: [
                { "currentRanks.minuteTokenRank": {$lt: 51} },
                { "currentRanks.fiveMinuteTokenRank": {$lt: 51} },
                { "currentRanks.fifteenMinuteTokenRank": {$lt: 51} },
                { "currentRanks.thirtyMinuteTokenRank": {$lt: 51} },
                { "currentRanks.hourlyTokenRank": {$lt: 51} },
                { "currentRanks.dailyTokenRank": {$lt: 51} },
                { "currentRanks.weeklyTokenRank": {$lt: 51} }
            ]
        }).lean();
        return data;
    } catch (error) {
        console.error("Error fetching data from DB:", error);
        throw error; // 向上抛出错误，由调用者处理
    }
}

// 刷新缓存的函数
async function refreshCache() {
    console.log(`Attempting to refresh cache at ${new Date().toLocaleTimeString()}...`);
    try {
        const newData = await fetchDataFromDB();
        cachedData = newData; // 替换旧数据
        lastRefreshTime = Date.now();
        console.log(`Cache refreshed successfully. Heap used: ${(process.memoryUsage().heapUsed / 1024 / 1024).toFixed(2)} MB`);
    } catch (error) {
        console.error("Failed to refresh cache:", error);
        // 刷新失败时，可以选择保留旧数据，或将其置空，取决于业务需求
        // cachedData = null;
    }
}

// 初始化缓存：首次加载数据并启动定时刷新
async function initializeCache() {
    await connectToMongo(); // 确保MongoDB连接
    console.log("Initializing cache: performing initial data load...");
    await refreshCache(); // 首次加载数据，确保应用启动时有数据
    setInterval(refreshCache, CACHE_REFRESH_INTERVAL); // 启动定时刷新
    console.log("Cache initialization complete. Refresh interval started.");
}

// 获取缓存数据的函数
function getCachedData() {
    return cachedData;
}

module.exports = {
    initializeCache,
    getCachedData
};

// app.js (Express主应用文件)
const express = require('express');
const { initializeCache, getCachedData } = require('./cacheService'); // 引入缓存服务模块
const app = express();
const PORT = 3000;

app.get('/api/data', (req, res) => {
    const data = getCachedData();
    if (data) {
        res.status(200).json(data);
    } else {
        // 如果缓存尚未加载或加载失败，返回服务不可用
        res.status(503).send({ message: "Data not yet available or failed to load. Please try again shortly." });
    }
});

// 启动服务器和缓存服务
async function startApp() {
    await initializeCache(); // 在服务器启动前初始化缓存
    app.listen(PORT, () => {
        console.log(`Server listening on port ${PORT}`);
    });
}

startApp();