Redis Strings

Introduction to Redis strings

Redis strings store sequences of bytes, including text, serialized objects, and binary arrays. As such, strings are the simplest type of value you can associate with a Redis key. They're often used for caching, but they support additional functionality that lets you implement counters and perform bitwise operations, too.

Since Redis keys are strings, when we use the string type as a value too, we are mapping a string to another string. The string data type is useful for a number of use cases, like caching HTML fragments or pages.

>_ Redis CLI

    > SET bike:1 Deimos
    OK
    > GET bike:1
    "Deimos"


public class StringSnippets
{
    public void run()
    {
        var redis = ConnectionMultiplexer.Connect("localhost:6379");
        var db = redis.GetDatabase();



        var res1 = db.StringSet("bike:1", "Deimos");
        Console.WriteLine(res1); // true
        var res2 = db.StringGet("bike:1");
        Console.WriteLine(res2); // Deimos


        var res3 = db.StringSet("bike:1", "bike", when: When.NotExists);
        Console.WriteLine(res3); // false
        Console.WriteLine(db.StringGet("bike:1"));
        var res4 = db.StringSet("bike:1", "bike", when: When.Exists);
        Console.WriteLine(res4); // true


        var res5 = db.StringSet(new KeyValuePair<RedisKey, RedisValue>[]
        {
            new ("bike:1", "Deimos"), new("bike:2", "Ares"), new("bike:3", "Vanth")
        });
        Console.WriteLine(res5);
        var res6 = db.StringGet(new RedisKey[] { "bike:1", "bike:2", "bike:3" });
        Console.WriteLine(res6);


        db.StringSet("total_crashes", 0);
        var res7 = db.StringIncrement("total_crashes");
        Console.WriteLine(res7); // 1
        var res8 = db.StringIncrement("total_crashes", 10);
        Console.WriteLine(res8);

    }
}

Java

package io.redis.examples;


import redis.clients.jedis.UnifiedJedis;
import redis.clients.jedis.params.SetParams;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class StringExample {
  public void run() {
    try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {

      String res1 = jedis.set("bike:1", "Deimos");
      System.out.println(res1); // OK
      String res2 = jedis.get("bike:1");
      System.out.println(res2); // Deimos


      Long res3 = jedis.setnx("bike:1", "bike");
      System.out.println(res3); // 0 (because key already exists)
      System.out.println(jedis.get("bike:1")); // Deimos (value is unchanged)
      String res4 = jedis.set("bike:1", "bike", SetParams.setParams().xx()); // set the value to "bike" if it
      // already
      // exists
      System.out.println(res4); // OK


      String res5 = jedis.mset("bike:1", "Deimos", "bike:2", "Ares", "bike:3", "Vanth");
      System.out.println(res5); // OK
      List<String> res6 = jedis.mget("bike:1", "bike:2", "bike:3");
      System.out.println(res6); // [Deimos, Ares, Vanth]


      jedis.set("total_crashes", "0");
      Long res7 = jedis.incr("total_crashes");
      System.out.println(res7); // 1
      Long res8 = jedis.incrBy("total_crashes", 10);
      System.out.println(res8); // 11

    }
  }
}

Python

import redis

r = redis.Redis(decode_responses=True)

res1 = r.set("bike:1", "Deimos")
print(res1)  # True
res2 = r.get("bike:1")
print(res2)  # Deimos


res3 = r.set("bike:1", "bike", nx=True)
print(res3)  # None
print(r.get("bike:1"))  # Deimos
res4 = r.set("bike:1", "bike", xx=True)
print(res4)  # True


res5 = r.mset({"bike:1": "Deimos", "bike:2": "Ares", "bike:3": "Vanth"})
print(res5)  # True
res6 = r.mget(["bike:1", "bike:2", "bike:3"])
print(res6)  # ['Deimos', 'Ares', 'Vanth']


r.set("total_crashes", 0)
res7 = r.incr("total_crashes")
print(res7)  # 1
res8 = r.incrby("total_crashes", 10)
print(res8)  # 11

As you can see using the SET and the GET commands are the way we set and retrieve a string value. Note that SET will replace any existing value already stored into the key, in the case that the key already exists, even if the key is associated with a non-string value. So SET performs an assignment.

Values can be strings (including binary data) of every kind, for instance you can store a jpeg image inside a value. A value can't be bigger than 512 MB.

The SET command has interesting options, that are provided as additional arguments. For example, I may ask SET to fail if the key already exists, or the opposite, that it only succeed if the key already exists:

>_ Redis CLI

    > set bike:1 bike nx
    (nil)
    > set bike:1 bike xx
    OK


public class StringSnippets
{
    public void run()
    {
        var redis = ConnectionMultiplexer.Connect("localhost:6379");
        var db = redis.GetDatabase();



        var res1 = db.StringSet("bike:1", "Deimos");
        Console.WriteLine(res1); // true
        var res2 = db.StringGet("bike:1");
        Console.WriteLine(res2); // Deimos


        var res3 = db.StringSet("bike:1", "bike", when: When.NotExists);
        Console.WriteLine(res3); // false
        Console.WriteLine(db.StringGet("bike:1"));
        var res4 = db.StringSet("bike:1", "bike", when: When.Exists);
        Console.WriteLine(res4); // true


        var res5 = db.StringSet(new KeyValuePair<RedisKey, RedisValue>[]
        {
            new ("bike:1", "Deimos"), new("bike:2", "Ares"), new("bike:3", "Vanth")
        });
        Console.WriteLine(res5);
        var res6 = db.StringGet(new RedisKey[] { "bike:1", "bike:2", "bike:3" });
        Console.WriteLine(res6);


        db.StringSet("total_crashes", 0);
        var res7 = db.StringIncrement("total_crashes");
        Console.WriteLine(res7); // 1
        var res8 = db.StringIncrement("total_crashes", 10);
        Console.WriteLine(res8);

    }
}

Java

package io.redis.examples;


import redis.clients.jedis.UnifiedJedis;
import redis.clients.jedis.params.SetParams;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class StringExample {
  public void run() {
    try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {

      String res1 = jedis.set("bike:1", "Deimos");
      System.out.println(res1); // OK
      String res2 = jedis.get("bike:1");
      System.out.println(res2); // Deimos


      Long res3 = jedis.setnx("bike:1", "bike");
      System.out.println(res3); // 0 (because key already exists)
      System.out.println(jedis.get("bike:1")); // Deimos (value is unchanged)
      String res4 = jedis.set("bike:1", "bike", SetParams.setParams().xx()); // set the value to "bike" if it
      // already
      // exists
      System.out.println(res4); // OK


      String res5 = jedis.mset("bike:1", "Deimos", "bike:2", "Ares", "bike:3", "Vanth");
      System.out.println(res5); // OK
      List<String> res6 = jedis.mget("bike:1", "bike:2", "bike:3");
      System.out.println(res6); // [Deimos, Ares, Vanth]


      jedis.set("total_crashes", "0");
      Long res7 = jedis.incr("total_crashes");
      System.out.println(res7); // 1
      Long res8 = jedis.incrBy("total_crashes", 10);
      System.out.println(res8); // 11

    }
  }
}

Python

import redis

r = redis.Redis(decode_responses=True)

res1 = r.set("bike:1", "Deimos")
print(res1)  # True
res2 = r.get("bike:1")
print(res2)  # Deimos


res3 = r.set("bike:1", "bike", nx=True)
print(res3)  # None
print(r.get("bike:1"))  # Deimos
res4 = r.set("bike:1", "bike", xx=True)
print(res4)  # True


res5 = r.mset({"bike:1": "Deimos", "bike:2": "Ares", "bike:3": "Vanth"})
print(res5)  # True
res6 = r.mget(["bike:1", "bike:2", "bike:3"])
print(res6)  # ['Deimos', 'Ares', 'Vanth']


r.set("total_crashes", 0)
res7 = r.incr("total_crashes")
print(res7)  # 1
res8 = r.incrby("total_crashes", 10)
print(res8)  # 11

There are a number of other commands for operating on strings. For example the GETSET command sets a key to a new value, returning the old value as the result. You can use this command, for example, if you have a system that increments a Redis key using INCR every time your web site receives a new visitor. You may want to collect this information once every hour, without losing a single increment. You can GETSET the key, assigning it the new value of "0" and reading the old value back.

The ability to set or retrieve the value of multiple keys in a single command is also useful for reduced latency. For this reason there are the MSET and MGET commands:

>_ Redis CLI

    > mset bike:1 "Deimos" bike:2 "Ares" bike:3 "Vanth"
    OK
    > mget bike:1 bike:2 bike:3
    1) "Deimos"
    2) "Ares"
    3) "Vanth"


public class StringSnippets
{
    public void run()
    {
        var redis = ConnectionMultiplexer.Connect("localhost:6379");
        var db = redis.GetDatabase();



        var res1 = db.StringSet("bike:1", "Deimos");
        Console.WriteLine(res1); // true
        var res2 = db.StringGet("bike:1");
        Console.WriteLine(res2); // Deimos


        var res3 = db.StringSet("bike:1", "bike", when: When.NotExists);
        Console.WriteLine(res3); // false
        Console.WriteLine(db.StringGet("bike:1"));
        var res4 = db.StringSet("bike:1", "bike", when: When.Exists);
        Console.WriteLine(res4); // true


        var res5 = db.StringSet(new KeyValuePair<RedisKey, RedisValue>[]
        {
            new ("bike:1", "Deimos"), new("bike:2", "Ares"), new("bike:3", "Vanth")
        });
        Console.WriteLine(res5);
        var res6 = db.StringGet(new RedisKey[] { "bike:1", "bike:2", "bike:3" });
        Console.WriteLine(res6);


        db.StringSet("total_crashes", 0);
        var res7 = db.StringIncrement("total_crashes");
        Console.WriteLine(res7); // 1
        var res8 = db.StringIncrement("total_crashes", 10);
        Console.WriteLine(res8);

    }
}

Java

package io.redis.examples;


import redis.clients.jedis.UnifiedJedis;
import redis.clients.jedis.params.SetParams;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class StringExample {
  public void run() {
    try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {

      String res1 = jedis.set("bike:1", "Deimos");
      System.out.println(res1); // OK
      String res2 = jedis.get("bike:1");
      System.out.println(res2); // Deimos


      Long res3 = jedis.setnx("bike:1", "bike");
      System.out.println(res3); // 0 (because key already exists)
      System.out.println(jedis.get("bike:1")); // Deimos (value is unchanged)
      String res4 = jedis.set("bike:1", "bike", SetParams.setParams().xx()); // set the value to "bike" if it
      // already
      // exists
      System.out.println(res4); // OK


      String res5 = jedis.mset("bike:1", "Deimos", "bike:2", "Ares", "bike:3", "Vanth");
      System.out.println(res5); // OK
      List<String> res6 = jedis.mget("bike:1", "bike:2", "bike:3");
      System.out.println(res6); // [Deimos, Ares, Vanth]


      jedis.set("total_crashes", "0");
      Long res7 = jedis.incr("total_crashes");
      System.out.println(res7); // 1
      Long res8 = jedis.incrBy("total_crashes", 10);
      System.out.println(res8); // 11

    }
  }
}

Python

import redis

r = redis.Redis(decode_responses=True)

res1 = r.set("bike:1", "Deimos")
print(res1)  # True
res2 = r.get("bike:1")
print(res2)  # Deimos


res3 = r.set("bike:1", "bike", nx=True)
print(res3)  # None
print(r.get("bike:1"))  # Deimos
res4 = r.set("bike:1", "bike", xx=True)
print(res4)  # True


res5 = r.mset({"bike:1": "Deimos", "bike:2": "Ares", "bike:3": "Vanth"})
print(res5)  # True
res6 = r.mget(["bike:1", "bike:2", "bike:3"])
print(res6)  # ['Deimos', 'Ares', 'Vanth']


r.set("total_crashes", 0)
res7 = r.incr("total_crashes")
print(res7)  # 1
res8 = r.incrby("total_crashes", 10)
print(res8)  # 11

When MGET is used, Redis returns an array of values.

Strings as counters

Even if strings are the basic values of Redis, there are interesting operations you can perform with them. For instance, one is atomic increment:

>_ Redis CLI

    > set total_crashes 0
    OK
    > incr total_crashes
    (integer) 1
    > incrby total_crashes 10
    (integer) 11


public class StringSnippets
{
    public void run()
    {
        var redis = ConnectionMultiplexer.Connect("localhost:6379");
        var db = redis.GetDatabase();



        var res1 = db.StringSet("bike:1", "Deimos");
        Console.WriteLine(res1); // true
        var res2 = db.StringGet("bike:1");
        Console.WriteLine(res2); // Deimos


        var res3 = db.StringSet("bike:1", "bike", when: When.NotExists);
        Console.WriteLine(res3); // false
        Console.WriteLine(db.StringGet("bike:1"));
        var res4 = db.StringSet("bike:1", "bike", when: When.Exists);
        Console.WriteLine(res4); // true


        var res5 = db.StringSet(new KeyValuePair<RedisKey, RedisValue>[]
        {
            new ("bike:1", "Deimos"), new("bike:2", "Ares"), new("bike:3", "Vanth")
        });
        Console.WriteLine(res5);
        var res6 = db.StringGet(new RedisKey[] { "bike:1", "bike:2", "bike:3" });
        Console.WriteLine(res6);


        db.StringSet("total_crashes", 0);
        var res7 = db.StringIncrement("total_crashes");
        Console.WriteLine(res7); // 1
        var res8 = db.StringIncrement("total_crashes", 10);
        Console.WriteLine(res8);

    }
}

Java

package io.redis.examples;


import redis.clients.jedis.UnifiedJedis;
import redis.clients.jedis.params.SetParams;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class StringExample {
  public void run() {
    try (UnifiedJedis jedis = new UnifiedJedis("redis://localhost:6379")) {

      String res1 = jedis.set("bike:1", "Deimos");
      System.out.println(res1); // OK
      String res2 = jedis.get("bike:1");
      System.out.println(res2); // Deimos


      Long res3 = jedis.setnx("bike:1", "bike");
      System.out.println(res3); // 0 (because key already exists)
      System.out.println(jedis.get("bike:1")); // Deimos (value is unchanged)
      String res4 = jedis.set("bike:1", "bike", SetParams.setParams().xx()); // set the value to "bike" if it
      // already
      // exists
      System.out.println(res4); // OK


      String res5 = jedis.mset("bike:1", "Deimos", "bike:2", "Ares", "bike:3", "Vanth");
      System.out.println(res5); // OK
      List<String> res6 = jedis.mget("bike:1", "bike:2", "bike:3");
      System.out.println(res6); // [Deimos, Ares, Vanth]


      jedis.set("total_crashes", "0");
      Long res7 = jedis.incr("total_crashes");
      System.out.println(res7); // 1
      Long res8 = jedis.incrBy("total_crashes", 10);
      System.out.println(res8); // 11

    }
  }
}

Python

import redis

r = redis.Redis(decode_responses=True)

res1 = r.set("bike:1", "Deimos")
print(res1)  # True
res2 = r.get("bike:1")
print(res2)  # Deimos


res3 = r.set("bike:1", "bike", nx=True)
print(res3)  # None
print(r.get("bike:1"))  # Deimos
res4 = r.set("bike:1", "bike", xx=True)
print(res4)  # True


res5 = r.mset({"bike:1": "Deimos", "bike:2": "Ares", "bike:3": "Vanth"})
print(res5)  # True
res6 = r.mget(["bike:1", "bike:2", "bike:3"])
print(res6)  # ['Deimos', 'Ares', 'Vanth']


r.set("total_crashes", 0)
res7 = r.incr("total_crashes")
print(res7)  # 1
res8 = r.incrby("total_crashes", 10)
print(res8)  # 11

The INCR command parses the string value as an integer, increments it by one, and finally sets the obtained value as the new value. There are other similar commands like INCRBY, DECR and DECRBY. Internally it's always the same command, acting in a slightly different way.

What does it mean that INCR is atomic? That even multiple clients issuing INCR against the same key will never enter into a race condition. For instance, it will never happen that client 1 reads "10", client 2 reads "10" at the same time, both increment to 11, and set the new value to 11. The final value will always be 12 and the read-increment-set operation is performed while all the other clients are not executing a command at the same time.

Limits

By default, a single Redis string can be a maximum of 512 MB.

Basic commands

Getting and setting Strings

SET stores a string value.
SETNX stores a string value only if the key doesn't already exist. Useful for implementing locks.
GET retrieves a string value.
MGET retrieves multiple string values in a single operation.

Managing counters

INCRBY atomically increments (and decrements when passing a negative number) counters stored at a given key.
Another command exists for floating point counters: INCRBYFLOAT.

Bitwise operations

To perform bitwise operations on a string, see the bitmaps data type docs.

See the complete list of string commands.

Performance

Most string operations are O(1), which means they're highly efficient. However, be careful with the SUBSTR, GETRANGE, and SETRANGE commands, which can be O(n). These random-access string commands may cause performance issues when dealing with large strings.

Alternatives

If you're storing structured data as a serialized string, you may also want to consider Redis hashes or JSON.

Learn more

Redis Strings Explained is a short, comprehensive video explainer on Redis strings.
Redis University's RU101 covers Redis strings in detail.

Redis Strings

Strings as counters

Limits

Basic commands

Getting and setting Strings

Managing counters

Bitwise operations

Performance

Alternatives

Learn more

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