redis-memolock

Redis Memolock for Node

A simple, fast, and reliable memolock for Node.js and TypeScript.

A MemoLock is a form of distributed caching with promises. It's like memoization, but since the cache is shared by multiple consumers, each key has a locking mechanism that ensures that multiple concurrent requests for the same resource don't cause unnecessary work.

- Stolen from https://github.com/kristoff-it/redis-memolock. Read more about memolock and why you want it there :)

Installation

npm i --save redis-memolock

Usage

import MemolockCache from 'redis-memolock';

const cache = new MemolockCache();

function getArticle(id: string) {
  return cache.get(
    // Key
    'article:' + id,

    // Cache for a minute
    { ttlMs: 60 * 1000 },

    // Fetch article normally
    () => getArticleFromDb(id),
  );
}

OR:

import MemolockCache from 'redis-memolock';

const cache = new MemolockCache();
const articleCache = cache.new(
  {
    getKey: (articleId: number) => 'article:' + articleId,
    ttlMs: 60 * 1000,
  },
  (id) => getArticleFromDb(id),
);

// Fetch the article at any time
articleCache.get(123);

// When article is updated
articleCache.delete(123);

---

API

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MemolockCache

MemolockCache.get(redisKey, opt, fetchFn)

Fetch a value from the cache. If the value is not in the cache, it will be fetched or wait for another process to fetch it.

• redisKey: The key to use in Redis.
• opt: Options for the cache (see below).
• fetchFn: A function that will be called to fetch the actual data if the cache is empty.

MemolockCache.delete(redisKey)

Identical to redis.del(redisKey).

MemolockCache.set(redisKey, value, opt)

Uses redis.set. Valid options are ttlMs and, optionally, encode (more about these in the "Options" section).

MemolockCache.new(opt, fetchFn)

Returns a CacheClient instance with two methods: get and delete.

• opt: Options for the cache (see below).
• fetchFn(getVal): A function that will be called to fetch the actual data if the cache is empty. It receives an argument which is the value passed into CacheClient.get.

---

CacheClient

CacheClient.get(keyVal, opt)

Passes keyVal into your provided getKey function to get the Redis key. opt will override any options passed to new. Otherwise works the same as MemolockCache.get.

CacheClient.delete(keyVal)

Pass keyVal into your provided getKey function to get the Redis key. Works the same as MemolockCache.delete.

CacheClient.set(keyVal, val)

Pass keyVal into your provided getKey function to get the Redis key. Simply uses the redis SET command with the provided value and client TTL.

Warning: A race condition can occur where a get that makes a fetch will overwrite your set. It's recommended that you only use set to warm up the cache, since it could be overwritten by the client's fetchFn before the key expires.

---

Options

Options are available on MemolockCache.get, MemolockCache.new, and CacheClient.get.

When using MemolockCache.get, you should always pass the same options for the same key to avoid unexpected behavior.

• ttlMs: How long before the cache expires in milliseconds. (Required for MemolockCache.get and CacheClient.new)
• lockTimeout: How long a lock is held. This should be longer than you expect a full fetch to take. If a process waits longer than lockTimeout for the cache to be populated, it will try again. (Default: 1000ms)
• maxAttempts: How many lock timeouts before giving up and throwing an error. (Default: 3)
• forceRefresh: Will ignore the cache and attempt to fetch the data again. Will not attempt a fetch if there's already a fetch in-progress. (Default: false)
• • getKey(keyVal): Function that converts a value to the cache key (Required, only on CacheClient.new)
• encode(dataFromFetch): Function that encodes the value to a string before storing it in the cache. (Default: JSON.stringify)
• decode(strFromRedis): Function that decodes the value from a string before returning it from the cache. (Default: JSON.parse)
• cacheIf(dataFromFetch): Function that determines whether to cache the value. NOTE: This will still publish the same value to all processes trying to fetch at the same time. It merely will not store the value in the cache. (Default: () => true)