IndexedDB LRU 缓存管理与淘汰实践

概述LRU 能在受限容量下保持高命中。本文提供写入访问时间、查询并淘汰的封装。结构与淘汰function openDB(name) { return new Promise((resolve, reject) => { const r = indexedDB.open(name, 1); r.onupgradeneeded = () => { const db = r.result; if (!db.objectStoreNames.contains('cache')) { const s = db.createObjectStore('cache', { keyPath:'key' }); s.createIndex('byLastUsed','lastUsed'); } }; r.onsuccess = () => resolve(r.result); r.onerror = () => reject(r.error); }); }

async function putCache(key, value) {

const db = await openDB('lru');

const tx = db.transaction('cache','readwrite');

tx.objectStore('cache').put({ key, value, lastUsed: Date.now() });

await new Promise((res, rej) => { tx.oncomplete = res; tx.onerror = () => rej(tx.error); });

db.close();

}

async function getCache(key) {

const db = await openDB('lru');

const tx = db.transaction('cache','readwrite');

const s = tx.objectStore('cache');

const req = s.get(key);

const rec = await new Promise((res, rej) => { req.onsuccess = () => res(req.result); req.onerror = () => rej(req.error); });

if (rec) s.put({ ...rec, lastUsed: Date.now() });

await new Promise((res, rej) => { tx.oncomplete = res; tx.onerror = () => rej(tx.error); });

db.close();

return rec ? rec.value : null;

}

async function evict(maxCount = 1000) {

const db = await openDB('lru');

const tx = db.transaction('cache','readwrite');

const s = tx.objectStore('cache');

const idx = s.index('byLastUsed');

const keys = [];

await new Promise((resolve, reject) => {

const req = s.openCursor();

req.onsuccess = e => { const c = e.target.result; if (c) { keys.push(c.key); c.continue(); } else resolve(); };

req.onerror = () => reject(req.error);

});

if (keys.length > maxCount) {

const toDelete = keys.length - maxCount;

let removed = 0;

const req2 = idx.openCursor();

await new Promise((resolve, reject) => {

req2.onsuccess = e => { const c = e.target.result; if (c && removed < toDelete) { s.delete(c.primaryKey); removed++; c.continue(); } else resolve(); };

req2.onerror = () => reject(req2.error);

});

}

await new Promise((res, rej) => { tx.oncomplete = res; tx.onerror = () => rej(tx.error); });

db.close();

}