PFCOUNT - Upstash Documentation

Use PFCOUNT to read the estimated number of distinct elements recorded in one or more HyperLogLogs.

With a single key the stored estimate is returned. With several keys the structures are merged on the fly and the cardinality of their union is returned, without modifying any of them, which is how you answer "how many unique users across these seven days" without double counting. The result is an approximation with a standard error of about 0.81%.

The multi-key form does real work on every call, so when the same union is read often it is cheaper to roll the sources up into one key with PFMERGE and count that.

Syntax#

PFCOUNT <key> [<key> ...]

Arguments#

Argument	Required	Repeatable	Description
`<key>`	Yes	Yes	Redis key targeted by the command.

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
RESP3	Integer

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

PFCOUNT my-key

@upstash/redis

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

upstash_redis

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

ioredis

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

redis-py

import osimport redisclient = redis.from_url(os.environ["REDIS_URL"])result = client.pfcount("my-key")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.PFCount(context.Background(), "my-key").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.pfcount("my-key");  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.pfcount(&["my-key"])?;    println!("{result:?}");    Ok(())}