redis

What is redis?

The npm package 'redis' is a Node.js client for Redis, a fast, open-source, in-memory key-value data store for use as a database, cache, message broker, and queue. The package allows Node.js applications to interact with Redis servers using an asynchronous, event-driven model.

What are redis's main functionalities?

Connecting to Redis

This code sample demonstrates how to connect to a Redis server using the redis npm package. It requires the package, creates a client, and listens for the 'connect' event to confirm the connection.

const redis = require('redis');
const client = redis.createClient();
client.on('connect', function() {
  console.log('Connected to Redis');
});

Setting and Getting Data

This code sample shows how to set a key-value pair in Redis and then retrieve the value associated with a key. The 'redis.print' callback is used to output the result of the 'set' operation.

client.set('key', 'value', redis.print);
client.get('key', function(err, reply) {
  console.log(reply); // prints 'value'
});

Working with Lists

This code sample illustrates how to work with Redis lists by pushing values to the end of a list and then retrieving the entire list.

client.rpush(['list', 'value1', 'value2'], redis.print);
client.lrange('list', 0, -1, function(err, reply) {
  console.log(reply); // prints ['value1', 'value2']
});

Publish/Subscribe

This code sample demonstrates the publish/subscribe capabilities of Redis. It creates a subscriber client that listens for messages on a channel and a publisher client that publishes a message to that channel.

const subscriber = redis.createClient();
const publisher = redis.createClient();
subscriber.on('message', function(channel, message) {
  console.log('Message: ' + message + ' on channel: ' + channel);
});
subscriber.subscribe('notification');
publisher.publish('notification', 'Hello, World!');

Transactions

This code sample shows how to use Redis transactions to execute multiple commands atomically using the 'multi' and 'exec' methods.

client.multi()
  .set('key', 'value')
  .incr('counter')
  .exec(function(err, replies) {
    console.log(replies); // prints results of all commands
  });

Other packages similar to redis

ioredis

ioredis is a robust, performance-focused, and full-featured Redis client for Node.js. It supports Redis Cluster, Sentinel, pipelining, Lua scripting, and more. Compared to the 'redis' package, ioredis offers a more modern interface with Promises support and better performance for certain operations.

node-redis

node-redis is another Redis client for Node.js that is designed to be easy to use. It may not have as many features as 'redis' or 'ioredis', but it provides a straightforward way to interact with Redis servers for simple use cases.

redis-mock

redis-mock is a library that simulates a Redis server for testing purposes. It implements most of the Redis commands and can be used as a drop-in replacement for the 'redis' package during testing, without the need for an actual Redis server.

README

redis - a node.js redis client

This is a complete Redis client for node.js. It is designed for node 0.2.2+ and redis 2.0.1+. It might not work on earlier versions of either, although it probably will.

This client supports all Redis commands, including MULTI and PUBLISH/SUBSCRIBE.

Install with:

npm install redis

Why?

node_redis works in the latest versions of node, is published in npm, and is very fast, particularly for small responses.

node_redis is designed with performance in mind. The included bench.js runs similar tests to redis-benchmark, included with the Redis distribution, and bench.js is as fast as redis-benchmark for some patterns and slower for others. node_redis has many lovingly hand-crafted optimizations for speed.

Usage

Simple example, included as example.js:

var redis = require("redis"),
    client = redis.createClient();

client.on("error", function (err) {
    console.log("Redis connection error to " + client.host + ":" + client.port + " - " + err);
});

client.set("string key", "string val", redis.print);
client.hset("hash key", "hashtest 1", "some value", redis.print);
client.hset(["hash key", "hashtest 2", "some other value"], redis.print);
client.hkeys("hash key", function (err, replies) {
    console.log(replies.length + " replies:");
    replies.forEach(function (reply, i) {
        console.log("    " + i + ": " + reply);
    });
    client.quit();
});

This will display:

mjr:~/work/node_redis (master)$ node example.js 
Reply: OK
Reply: 0
Reply: 0
2 replies:
    0: hashtest 1
    1: hashtest 2
mjr:~/work/node_redis (master)$ 

Sending Commands

Each Redis command is exposed as a function on the client object. All functions take either take either an args Array plus optional callback Function or a variable number of individual arguments followed by an optional callback. Here is an example of passing an array of arguments and a callback:

client.mset(["test keys 1", "test val 1", "test keys 2", "test val 2"], function (err, res) {});

Here is that same call in the second style:

client.mset("test keys 1", "test val 1", "test keys 2", "test val 2", function (err, res) {});

Note that in either form the callback is optional:

client.set("some key", "some val");
client.set(["some other key", "some val"]);

For a list of Redis commands, see Redis Command Reference

The commands can be specified in uppercase or lowercase for convenience. client.get() is the same as client.GET().

Minimal parsing is done on the replies. Commands that return a single line reply return JavaScript Strings, integer replies return JavaScript Numbers, "bulk" replies return node Buffers, and "multi bulk" replies return a JavaScript Array of node Buffers. HGETALL returns an Object with Buffers keyed by the hash keys.

API

Connection Events

client will emit some events about the state of the connection to the Redis server.

"connect"

client will emit connect when a connection is established to the Redis server.

Commands issued before the connect event are queued, then replayed when a connection is established.

"error"

client will emit error when encountering an error connecting to the Redis server.

Note that "error" is a special event type in node. If there are no listeners for an "error" event, node will exit. This is usually what you want, but it can lead to some cryptic error messages like this:

mjr:~/work/node_redis (master)$ node example.js 

node.js:50
    throw e;
    ^
Error: ECONNREFUSED, Connection refused
    at IOWatcher.callback (net:870:22)
    at node.js:607:9

Not very useful in diagnosing the problem, but if your program isn't ready to handle this, it is probably the right thing to just exit.

client will also emit error if an exception is thrown inside of node_redis for whatever reason. In the future, there will be a better way to distinguish these error types.

"end"

client will emit end when an established Redis server connection has closed.

"drain"

client will emit drain when the TCP connection to the Redis server has been buffering, but is now writable. This event can be used to stream commands in to Redis and adapt to backpressure. Right now, you need to check client.command_queue.length to decide when to reduce your send rate. Then you can resume sending when you get drain.

"idle"

client will emit idle when there are no outstanding commands that are awaiting a response.

redis.createClient(port, host)

Create a new client connection. port defaults to 6379 and host defaults to 127.0.0.1. If you have Redis running on the same computer as node, then the defaults are probably fine.

createClient returns a RedisClient object that is named client in all of the examples here.

client.end()

Forcibly close the connection to the Redis server. Note that this does not wait until all replies have been parsed. If you want to exit cleanly, call client.quit() to send the QUIT command after you have handled all replies.

This example closes the connection to the Redis server before the replies have been read. You probably don't want to do this:

var redis = require("redis"),
    client = redis.createClient();

client.set("foo_rand000000000000", "some fantastic value");
client.get("foo_rand000000000000", function (err, reply) {
    console.log(reply.toString());
});
client.end();

client.end() is useful for timeout cases where something is stuck or taking too long and you want to start over.

Publish / Subscribe

Here is a simple example of the API for publish / subscribe. This program opens two client connections, subscribes to a channel on one of them, and publishes to that channel on the other:

var redis = require("redis"),
    client1 = redis.createClient(), client2 = redis.createClient(),
    msg_count = 0;

client1.on("subscribe", function (channel, count) {
    client2.publish("a nice channel", "I am sending a message.");
    client2.publish("a nice channel", "I am sending a second message.");
    client2.publish("a nice channel", "I am sending my last message.");
});

client1.on("message", function (channel, message) {
    console.log("client1 channel " + channel + ": " + message);
    msg_count += 1;
    if (msg_count === 3) {
        client1.unsubscribe();
        client1.end();
        client2.end();
    }
});

client1.incr("did a thing");
client1.subscribe("a nice channel");

When a client issues a SUBSCRIBE or PSUBSCRIBE, that connection is put into "pub/sub" mode. At that point, only commands that modify the subscription set are valid. When the subscription set is empty, the connection is put back into regular mode.

If you need to send regular commands to Redis while in pub/sub mode, just open another connection.

Pub / Sub Events

If a client has subscriptions active, it may emit these events:

"message" (channel, message)

Client will emit message for every message received that matches an active subscription. Listeners are passed the channel name as channel and the message Buffer as message.

"pmessage" (pattern, channel, message)

Client will emit pmessage for every message received that matches an active subscription pattern. Listeners are passed the original pattern used with PSUBSCRIBE as pattern, the sending channel name as channel, and the message Buffer as message.

"subscribe" (channel, count)

Client will emit subscribe in response to a SUBSCRIBE command. Listeners are passed the channel name as channel and the new count of subscriptions for this client as count.

"psubscribe" (pattern, count)

Client will emit psubscribe in response to a PSUBSCRIBE command. Listeners are passed the original pattern as pattern, and the new count of subscriptions for this client as count.

"unsubscribe" (channel, count)

Client will emit unsubscribe in response to a UNSUBSCRIBE command. Listeners are passed the channel name as channel and the new count of subscriptions for this client as count. When count is 0, this client has left pub/sub mode and no more pub/sub events will be emitted.

"punsubscribe" (pattern, count)

Client will emit punsubscribe in response to a PUNSUBSCRIBE command. Listeners are passed the channel name as channel and the new count of subscriptions for this client as count. When count is 0, this client has left pub/sub mode and no more pub/sub events will be emitted.

client.multi([commands])

MULTI commands are queued up until an EXEC is issued, and then all commands are run atomically by Redis. The interface in node_redis is to return an individual Multi object by calling client.multi().

var redis  = require("./index"),
    client = redis.createClient(), set_size = 20;

client.sadd("bigset", "a member");
client.sadd("bigset", "another member");

while (set_size > 0) {
    client.sadd("bigset", "member " + set_size);
    set_size -= 1;
}

// multi chain with an individual callback
client.multi()
    .scard("bigset")
    .smembers("bigset")
    .keys("*", function (err, replies) {
        client.mget(replies, redis.print);
    })
    .dbsize()
    .exec(function (err, replies) {
        console.log("MULTI got " + replies.length + " replies");
        replies.forEach(function (reply, index) {
            console.log("Reply " + index + ": " + reply.toString());
        });
    });

client.multi() is a constructor that returns a Multi object. Multi objects share all of the same command methods as client objects do. Commands are queued up inside the Multi object until Multi.exec() is invoked.

You can either chain together MULTI commands as in the above example, or you can queue individual commands while still sending regular client command as in this example:

var redis  = require("redis"),
    client = redis.createClient(), multi;

// start a separate multi command queue 
multi = client.multi();
multi.incr("incr thing", redis.print);
multi.incr("incr other thing", redis.print);

// runs immediately
client.mset("incr thing", 100, "incr other thing", 1, redis.print);

// drains multi queue and runs atomically
multi.exec(function (err, replies) {
    console.log(replies); // 101, 2
});

// you can re-run the same transaction if you like
multi.exec(function (err, replies) {
    console.log(replies); // 102, 3
    client.quit();
});

In addition to adding commands to the MULTI queue individually, you can also pass an array of commands and arguments to the constructor:

var redis  = require("redis"),
    client = redis.createClient(), multi;

client.multi([
    ["mget", "multifoo", "multibar", redis.print],
    ["incr", "multifoo"],
    ["incr", "multibar"]
]).exec(function (err, replies) {
    console.log(replies);
});

Extras

Some other things you might like to know about.

redis.print()

A handy callback function for displaying return values when testing. Example:

var redis = require("redis"),
    client = redis.createClient();

client.on("connect", function () {
    client.set("foo_rand000000000000", "some fantastic value", redis.print);
    client.get("foo_rand000000000000", redis.print);
});

This will print:

Reply: OK
Reply: some fantastic value

Note that this program will not exit cleanly because the client is still connected.

redis.debug_mode

Boolean to enable debug mode and protocol tracing.

var redis = require("redis"),
    client = redis.createClient();

redis.debug_mode = true;

client.on("connect", function () {
    client.set("foo_rand000000000000", "some fantastic value");
});

This will display:

mjr:~/work/node_redis (master)$ node ~/example.js 
send command: *3
$3
SET
$20
foo_rand000000000000
$20
some fantastic value

on_data: +OK

send command is data sent into Redis and on_data is data received from Redis.

client.send_command(command_name, args, callback)

Used internally to send commands to Redis. For convenience, nearly all commands that are published on the Redis Wiki have been added to the client object. However, if I missed any, or if new commands are introduced before this library is updated, you can use send_command() to send arbitrary commands to Redis.

All commands are sent as multi-bulk commands. args can either be an Array of arguments, or individual arguments, or omitted completely.

client.connected

Boolean tracking the state of the connection to the Redis server.

client.command_queue.length

The number of commands that have been sent to the Redis server but not yet replied to. You can use this to enforce some kind of maximum queue depth for commands while connected.

Don't mess with client.command_queue though unless you really know what you are doing.

client.offline_queue.length

The number of commands that have been queued up for a future connection. You can use this to enforce some kind of maximum queue depth for pre-connection commands.

client.retry_delay

Current delay in milliseconds before a connection retry will be attempted. This starts at 250.

client.retry_backoff

Multiplier for future retry timeouts. This should be larger than 1 to add more time between retries. Defaults to 1.7. The default initial connection retry is 250, so the second retry will be 425, followed by 723.5, etc.

TODO

Many common uses of Redis are fine with JavaScript Strings, and Strings are faster than Buffers. We should get a way to use Strings if binary-safety isn't a concern. Also, dealing with Buffer results is kind of annoying.

Stream large set/get into and out of Redis.

Performance can be better for very large values.

I think there are more performance improvements left in there for smaller values, especially for large lists of small values.

Also

This library might still have some bugs in it, but it seems to be quite useful for a lot of people at this point. There are other Redis libraries available for node, and they might work better for you.

Comments and patches welcome.

Contributors

Some people have have added features and fixed bugs in node_redis other than me.

In order of first contribution, they are:

• Tim Smart
• TJ Holowaychuk
• Rick Olson
• Orion Henry
• Hank Sims
• Aivo Paas

Thanks.

LICENSE - "MIT License"

Copyright (c) 2010 Matthew Ranney, http://ranney.com/

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.