SETNX - Upstash Documentation

Warning

Prefer SET with the NX argument in new code: SET <key> <value> NX.

Use SETNX to set a value only if the key does not already exist.

The reply is 1 when the key was created and 0 when it was already there and nothing was written. The check and the write are atomic, so exactly one of several racing clients succeeds.

That makes it the classic lock primitive, but on its own it is an incomplete one: a client that fails after acquiring leaves the key behind forever. Prefer SET key value NX EX <ttl>, which claims the key and attaches an expiration in the same step, and release the lock with DELEX so you only delete it while you still own it.

Syntax#

SETNX <key> <value>

Arguments#

Argument	Required	Repeatable	Description
`<key>`	Yes	No	Redis key targeted by the command.
`<value>`	Yes	No	String value to store.

Response#

The reply reports the result of the operation. Error replies have the same shape in RESP2 and RESP3 and are surfaced as exceptions by the SDKs below.

Protocol	Reply
RESP2	Integer: `1` if the key was set, `0` if it already exists
RESP3	Integer: `1` if the key was set, `0` if it already exists

Note

Client libraries often decode bulk strings, maps, sets, and numeric strings into language-native values. The table describes the Redis wire reply.

Examples#

TCP examples use the TLS REDIS_URL from the Upstash console. REST examples use UPSTASH_REDIS_REST_URL and UPSTASH_REDIS_REST_TOKEN.

Redis CLI

SETNX my-key value

@upstash/redis

import { Redis } from "@upstash/redis";const redis = Redis.fromEnv();const result = await redis.setnx("my-key", "value");console.log(result);

upstash_redis

from upstash_redis import Redisredis = Redis.from_env()result = redis.setnx("my-key", "value")print(result)

ioredis

import Redis from "ioredis";const redis = new Redis(process.env.REDIS_URL!);const result = await redis.setnx("my-key", "value");console.log(result);

node-redis

import { createClient } from "redis";const client = await createClient({ url: process.env.REDIS_URL })  .on("error", console.error)  .connect();const result = await client.setNX("my-key", "value");console.log(result);

redis-py

import osimport redisclient = redis.from_url(os.environ["REDIS_URL"])result = client.setnx("my-key", "value")print(result)

go-redis

package mainimport (    "context"    "fmt"    "os"    "github.com/redis/go-redis/v9")func main() {    opts, err := redis.ParseURL(os.Getenv("REDIS_URL"))    if err != nil {        panic(err)    }    client := redis.NewClient(opts)    result, err := client.SetNX(context.Background(), "my-key", "value", 0).Result()    if err != nil {        panic(err)    }    fmt.Println(result)}

jedis

import java.net.URI;import redis.clients.jedis.Jedis;try (Jedis jedis = new Jedis(new URI(System.getenv("REDIS_URL")))) {  Object result = jedis.setnx("my-key", "value");  System.out.println(result);}

redis-rs

use redis::TypedCommands;fn main() -> redis::RedisResult<()> {    let url = std::env::var("REDIS_URL").expect("REDIS_URL is not set");    let client = redis::Client::open(url)?;    let mut connection = client.get_connection()?;    let result = connection.set_nx("my-key", "value")?;    println!("{result:?}");    Ok(())}