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

redis - a node.js redis client

This is a complete Redis client for node.js. It supports all Redis commands, including many recently added commands like EVAL from experimental Redis server branches.

Install with:

npm install redis

Pieter Noordhuis has provided a binding to the official hiredis C library, which is non-blocking and fast. To use hiredis, do:

npm install hiredis redis

If hiredis is installed, node_redis will use it by default. Otherwise, a pure JavaScript parser will be used.

If you use hiredis, be sure to rebuild it whenever you upgrade your version of node. There are mysterious failures that can happen between node and native code modules after a node upgrade.

Usage

Simple example, included as examples/simple.js:

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

client.on("error", function (err) {
    console.log("Error " + 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)$

Performance

Here are typical results of multi_bench.js which is similar to redis-benchmark from the Redis distribution. It uses 50 concurrent connections with no pipelining.

JavaScript parser:

PING: 20000 ops 42283.30 ops/sec 0/5/1.182
SET: 20000 ops 32948.93 ops/sec 1/7/1.515
GET: 20000 ops 28694.40 ops/sec 0/9/1.740
INCR: 20000 ops 39370.08 ops/sec 0/8/1.269
LPUSH: 20000 ops 36429.87 ops/sec 0/8/1.370
LRANGE (10 elements): 20000 ops 9891.20 ops/sec 1/9/5.048
LRANGE (100 elements): 20000 ops 1384.56 ops/sec 10/91/36.072

hiredis parser:

PING: 20000 ops 46189.38 ops/sec 1/4/1.082
SET: 20000 ops 41237.11 ops/sec 0/6/1.210
GET: 20000 ops 39682.54 ops/sec 1/7/1.257
INCR: 20000 ops 40080.16 ops/sec 0/8/1.242
LPUSH: 20000 ops 41152.26 ops/sec 0/3/1.212
LRANGE (10 elements): 20000 ops 36563.07 ops/sec 1/8/1.363
LRANGE (100 elements): 20000 ops 21834.06 ops/sec 0/9/2.287

The performance of node_redis improves dramatically with pipelining, which happens automatically in most normal programs.

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.

"ready"

client will emit ready a connection is established to the Redis server and the server reports that it is ready to receive commands. Commands issued before the ready event are queued, then replayed just before this event is emitted.

"connect"

client will emit connect at the same time as it emits ready unless client.options.no_ready_check is set. If this options is set, connect will be emitted when the stream is connected, and then you are free to try to send commands.

"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. It would be nice to distinguish these two cases.

"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, options)

Create a new client connection. port defaults to 6379 and host defaults to 127.0.0.1. If you have redis-server running on the same computer as node, then the defaults for port and host are probably fine. options in an object with the following possible properties:

parser: which Redis protocol reply parser to use. Defaults to hiredis if that module is installed. This may also be set to javascript.
return_buffers: defaults to false. If set to true, then bulk data replies will be returned as node Buffer objects instead of JavaScript Strings.

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

client.auth(password, callback)

When connecting to Redis servers that require authentication, the AUTH command must be sent as the first command after connecting. This can be tricky to coordinate with reconnections, the ready check, etc. To make this easier, client.auth() stashes password and will send it after each connection, including reconnections. callback is invoked only once, after the response to the very first AUTH command sent.

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.

Friendlier hash commands

Most Redis commands take a single String or an Array of Strings as arguments, and replies are sent back as a single String or an Array of Strings. When dealing with hash values, there are a couple of useful exceptions to this.

client.hgetall(hash)

The reply from an HGETALL command will be converted into a JavaScript Object by node_redis. That way you can interact with the responses using JavaScript syntax.

Example:

client.hmset("hosts", "mjr", "1", "another", "23", "home", "1234");
client.hgetall("hosts", function (err, obj) {
    console.dir(obj);
});

Output:

{ mjr: '1', another: '23', home: '1234' }

client.hmset(hash, obj, [callback])

Multiple values in a hash can be set by supplying an object:

client.HMSET(key2, {
    "0123456789": "abcdefghij",
    "some manner of key": "a type of value"
});

The properties and values of this Object will be set as keys and values in the Redis hash.

client.hmset(hash, key1, val1, ... keyn, valn, [callback])

Multiple values may also be set by supplying a list:

client.HMSET(key1, "0123456789", "abcdefghij", "some manner of key", "a type of value");

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.

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);
});

Monitor mode

Redis supports the MONITOR command, which lets you see all commands received by the Redis server across all client connections, including from other client libraries and other computers.

After you send the MONITOR command, no other commands are valid on that connection. node_redis will emit a monitor event for every new monitor message that comes across. The callback for the monitor event takes a timestamp from the Redis server and an array of command arguments.

Here is a simple example:

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

client.monitor(function (err, res) {
    console.log("Entering monitoring mode.");
});

client.on("monitor", function (time, args) {
    console.log(time + ": " + util.inspect(args));
});

Extras

Some other things you might like to know about.

client.server_info

After the ready probe completes, the results from the INFO command are saved in the client.server_info object.

The versions key contains an array of the elements of the version string for easy comparison.

> client.server_info.redis_version
'2.3.0'
> client.server_info.versions
[ 2, 3, 0 ]

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

Better tests for monitor mode, auth, disconnect/reconnect, and all combinations thereof.

Stream large set/get values into and out of Redis. Otherwise the entire value must be in node's memory.

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.

Contributors

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

In order of first contribution, they are:

Thanks.

LICENSE - "MIT License"

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.

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Package last updated on 31 Jul 2011

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