@creditkarma/memcached

A fully featured Memcached API client, supporting both single and clustered Memcached servers through consistent hashing and failover/failure. Memcached is rewrite of nMemcached, which will be deprecated in the near future.

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Readme

Notice

This is forked from 3rd-eden/memcached. This fork has been rewritten in TypeScript.

Memcached

memcached is a fully featured Memcached client for Node.js. memcached is built with scaling, high availability and exceptional performance in mind. We use consistent hashing to store the data across different nodes. Consistent hashing is a scheme that provides a hash table functionality in a way that adding or removing a server node does not significantly change the mapping of the keys to server nodes. The algorithm that is used for consistent hashing is the same as libketama.

There are different ways to handle errors for example, when a server becomes unavailable you can configure the client to see all requests to that server as cache misses until it goes up again. It's also possible to automatically remove the affected server from the consistent hashing algorithm or provide memcached with a failover server that can take the place of the unresponsive server.

When these issues occur the memcached client will emit different events where you can subscribe to containing detailed information about the issues.

The client is configurable on different levels. There's a global configuration that you update so all your Memcached clusters will use the same failure configuration for example, but it's also possible to overwrite these changes per memcached instance.

protocol

As in other databases and message queues, this module uses the ASCII protocol to communicate with the server, which means that you can see what is send over the wire. For debugging this is easier for both the users and the developers however this also means that SASL auth is not supported because it demands the binary protocol.

Installation

npm install @creditkarma/memcached

Setting up the client

We can setup the client in two ways,

  1. callback styled client
  2. promise styled client.

For using a callback styled client, please refer to doc

The constructor of the promise style memcached client take 2 different arguments server locations (mandatory) and options (optional). Syntax:

import { IMemcachedConfig, MemcachedClient, Servers } from '@creditkarma/memcached'
const servers: Servers = ['192.168.0.102:11211'];
const options: IMemcachedConfig = {};
const memcached: MemcachedClient = new MemcachedClient(servers, options);

Server locations

The server locations is designed to work with different formats. These formats are all internally parsed to the correct format so our consistent hashing scheme can work with it. You can either use:

  1. String, this only works if you are running a single server instance of Memcached. It's as easy a suppling a string in the following format: hostname:port. For example 192.168.0.102:11211 This would tell the client to connect to host 192.168.0.102 on port number 11211.

  2. Array, if you are running a single server you would only have to supply one item in the array. The array format is particularly useful if you are running a cluster of Memcached servers. This will allow you to spread the keys and load between the different servers. Giving you higher availability when one of your Memcached servers goes down.

  3. Object, when running a cluster of Memcached servers, some servers may allocate different amounts of memory, e.g. 128, 512, and 128mb. While by default all servers are equally important and dispatch consistently the keys between the servers (33/33/33%), it is possible to send more keys in servers having more memory. To do so, define an object whose key represents the server location and whose value represents a server weight, the default weight for a server being 1; so, for instance { '192.168.0.102:11211': 1, '192.168.0.103:11211': 2, '192.168.0.104:11211': 1 } distributes 50% of the keys on server 103, but only 25% on 104 and 25% on 102.

To implement one of the above formats, your constructor would look like one of this:

const servers: Servers = { '192.168.0.102:11211': 1, '192.168.0.103:11211': 2, '192.168.0.104:11211': 1 };
const memcached: MemcachedClient = new MemcachedClient(servers);

const servers: Servers = [ '192.168.0.102:11211', '192.168.0.103:11211', '192.168.0.104:11211' ];
const memcached: MemcachedClient = new MemcachedClient(servers);

const servers: Servers = '192.168.0.102:11211';
const memcached: MemcachedClient = new MemcachedClient(servers);

Options

Memcached accepts two option schemes. The first one inherits of all Memcached server instances while the second one is client specific and overwrites the globals. To define these options, Memcached server uses the same properties:

  • defaultTTL: 600, the default ttl (in secondes) for new cache entries
  • maxKeySize: 250, the maximum key size allowed.
  • maxExpiration: 2592000, the maximum expiration time of keys (in seconds).
  • maxValue: 1048576, the maximum size of a value.
  • poolSize: 10, the maximum size of the connection pool.
  • algorithm: md5, the hashing algorithm used to generate the hashRing values.
  • reconnect: 18000000, the time between reconnection attempts (in milliseconds).
  • timeout: 5000, the time after which Memcached sends a connection timeout (in milliseconds).
  • retries: 5, the number of socket allocation retries per request.
  • failures: 5, the number of failed-attempts to a server before it is regarded as 'dead'.
  • retry: 30000, the time between a server failure and an attempt to set it up back in service.
  • remove: false, if true, authorizes the automatic removal of dead servers from the pool.
  • failOverServers: undefined, an array of server_locations to replace servers that fail and that are removed from the consistent hashing scheme.
  • keyCompression: true, whether to use md5 as hashing scheme when keys exceed maxKeySize.
  • idle: 5000, the idle timeout for the connections.

Example usage:

const servers: Servers = 'localhost:11211';
const options: IMemcachedConfig = {
  retries : 10,
  retry : 10000,
  remove : true,
  failOverServers : [ '192.168.0.103:11211' ]
};

const memcached: MemcachedClient = new MemcachedClient(servers, options);

API

Public methods

memcached.get Get the value for the given key.

  • key: String, the key
  • decode: function, (optional) function to decode the string reference
          to a class object
    
const readValue = await memcached.get(key).catch((err) => {return err});
// OR
const readValue = await memcached.get(key, decode).catch((err) => {return err});

memcached.gets Get the value and the CAS id.

  • key: String, the key
const result = await memcached.gets('foo');

memcached.getMulti Retrieves a bunch of values from multiple keys.

  • keys: Array, all the keys that needs to be fetched
  • callback: Function, the callback.
let result = await memcached.getMulti(['foo1', 'foo2', 'foo3']);

memcached.getWithDefault Gets the value for the given key or a configured default if the key does not exist in the cache.

  • key: String, the key
const readValue = await memcached.getWithDefault(key, 10)

memcached.set Stores a new value in Memcached.

  • key: String the name of the key
  • value: Mixed Either a buffer, JSON, number or string that you want to store.
  • lifetime: Number, (optional) how long the data needs to be stored
            measured in `seconds`
    
const key = 'key'
const value = 1
const customTTL = 60 // In seconds
await memcached.set(key, value)
// OR
await memcached.set(key, value, customTTL)

memcached.encodeAndSet Stores reference to class object in Memcached.

  • key: String the name of the key
  • value: Mixed Either a buffer, JSON, number or string that you want to store.
  • encoder: Function that encodes the properties of class into a string.
  • lifetime: Number, (optional) how long the data needs to be stored
            measured in `seconds`
    
const key = 'key'
const value = 1
const customTTL = 60 // In seconds
await memcached.encodeAndSet(key, value, encoder)
// OR
await memcached.encodeAndSet(key, value, encoder, customTTL)

memcached.cas Add the value, only if it matches the given CAS value.

  • key: String the name of the key
  • value: Mixed Either a buffer, JSON, number or string that you want to store.
  • cas: String the CAS value
  • lifetime: Number, (optional) how long the data needs to be replaced
            measured in `seconds`
    
const result = await memcached.gets(key)
const cas = result.cas
const newValue = 20
const customTTL = 60
await memcached.cas(key, newValue, cas)
// OR
await memcached.cas(key, newValue, cas, customTTL)

memcached.encodeAndCas Add the reference to class object, only if it matches the given CAS value.

  • key: String the name of the key
  • value: Mixed Either a buffer, JSON, number or string that you want to store.
  • cas: String the CAS value
  • encoder: Function that encodes the properties of class into a string.
  • lifetime: Number, (optional) how long the data needs to be replaced
            measured in `seconds`
    
const result = await memcached.gets(key)
const cas = result.cas
const newValue = 20
const customTTL = 60
await memcached.encodeAndCas(key, newValue, cas, encoder)
// OR
await memcached.encodeAndCas(key, newValue, cas, encoder, customTTL)

memcached.del Remove the key from memcached.

  • key: String the name of the key
await memcached.del(key).catch((err) => { console.error(err); return })

memcached.flush Flushes the memcached server.

await memcached.flush().catch((err) => { console.error(err); return })

memcached.end Closes all active memcached connections. This is a synchronous call

memcached.end()

memcached.addListener Add custom event listener for handling events memcached client emits.

function reconnectingHandler(details) {
  console.log("Total downtime caused by server " + details.server + " :" + details.totalDownTime + "ms")
}
function failureHandler(details) {
  console.log("Server " + details.server + "went down due to: " + details.messages.join( '' ))
}
await memcached.addListener('failure', failureHandler)
await memcached.addListener('reconnecting', reconnectingHandler)

Compatibility

For compatibility with other libmemcached clients they need to have the behavior ketama_weighted set to true and the hash set to the same as node-memcached's algorithm.

Due to client dependent type flags it is unlikely that any types other than string will work.

Contributors

This project wouldn't be possible without the hard work of our amazing contributors. See the contributors tab in Github for an up to date list of contributors.

Thanks for all your hard work on this project!

License

The driver is released under the MIT license. See the LICENSE for more information.

If you find any bugs or have a feature request, please open an issue on github!

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