Stale-multi-cache NPM

stale-multi-cache

Multi level cache that always prefers stale data

The middleware functionality was ported from apicache. If you don't need the other features of this caching library that is a more full-featured library.

Usage

This library is undergoing API changes at the moment. We will follow semantic versioning so once we change the publicly exposed methods you'll see a jump to 2.0.0 and beyond.

Right now the main cache.js file needs a lot of cleanup, messy and too many responsibilities. However the functionality of wrap and middleware are highly tested and probably good to go.

var Cache = require('stale-multi-cache');
var Redis = require('ioredis');
var redis = new Redis();

// Create the cache
var cache = new Cache([
  new Cache.LRUMemoryStore({max:500}),
  new Cache.RedisStore(redis)
]);

function getUser(user) {
  // really really slow function
  return {};
}

// Even with a stale TTL of 10, this cache will always send stale data,
// but do a background update of the data after the data expires.
// We're setting the expire TTL to 86400 at that point we'll HAVE to refresh.
function cachedGetUser(user) {
  return cache.wrap('user:'+user, function() {
    return getUser(user);
  }, {
    staleTTL: 10,
    expireTTL: 86400
  });
}

// Now we can use the cachedGetUser
app.get('/user', function(req, res) {
  return cachedGetUser('kelsin').then(function(user) {
    return res.json({user:user});
  });
});

// We can also use the middleware to automatically cache responses
app.use(cache.middleware());
app.get('/cached', function(req, res) {
  // some long response
});

Stores

Store	Description
`NoopStore`	Store that never stores anything, for testing purposes
`ErrorStore`	Store that never stores anything and errors on sets, for testing purposes
`SimpleMemoryStore`	Object store, for testing purposes
`LRUStore`	Memory store that uses lru-cache
`RedisStore`	Redis store that uses any ioredis compatible client

Why?

I often need caches that are double buffered but where TTL is more of an update interval than a hard expire. I want to use LRU based stores and update at set times but always keep stale data. I never want most web caches to expire. I'd rather have old data on the site than no data on the site. This cache provides that.