HSCAN - Upstash Documentation

Use HSCAN to iterate the fields of a hash in batches instead of reading it all at once.

Each call takes a cursor and returns the next cursor together with a batch of field and value pairs. Start at cursor 0 and keep calling with the cursor from the previous reply until the server returns 0, which ends the iteration. Because each call does a bounded amount of work, this avoids the long single reply that HGETALL produces on a large hash.

MATCH filters field names with a glob-style pattern, COUNT hints at how much work each call should do, and NOVALUES returns field names only, which is noticeably cheaper when values are large and you do not need them. Filtering is applied after a batch has been read, so a call can return nothing while the cursor is still non-zero: only a cursor of 0 means the iteration is over. Fields present for the whole iteration are returned at least once, and fields added or removed while it runs may or may not appear.

Syntax#

HSCAN <key> <cursor> [MATCH <pattern>] [COUNT <count>] [NOVALUES]

Arguments#

Argument	Required	Repeatable	Description
`<key>`	Yes	No	Redis key targeted by the command.
`<cursor>`	Yes	No	Cursor returned by the previous call; start at `0`.
`MATCH <pattern>`	No	No	Return only elements matching this glob-style pattern.
`COUNT <count>`	No	No	Hint for how much work each iteration should do.
`NOVALUES`	No	No	Return only field names, without their values.

Important points#

This operation can inspect a large part of the database. Prefer cursor-based scans where possible and avoid unbounded use on hot paths.
The cursor is opaque. Start with 0 and continue until the server returns cursor 0; a single iteration may return no elements.

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	Two-element array: cursor and flat field/value array, or field array with `NOVALUES`
RESP3	Two-element array: cursor and flat field/value array, or field array with `NOVALUES`

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

HSCAN my-key 0

@upstash/redis

import { Redis } from "@upstash/redis";const redis = Redis.fromEnv();await redis.hset("key", {  id: 1,  username: "chronark",  name: "andreas" });const [newCursor, fields] = await redis.hscan("key", 0);console.log(newCursor); // likely `0` since this is a very small hashconsole.log(fields); // ["id", 1, "username", "chronark", "name", "andreas"]

upstash_redis

from upstash_redis import Redisredis = Redis.from_env()result = redis.hscan("my-key", 0)print(result)

ioredis

import Redis from "ioredis";const redis = new Redis(process.env.REDIS_URL!);const result = await redis.hscan("my-key", "0");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.hScan("my-key", "0");console.log(result);

redis-py

import osimport redisclient = redis.from_url(os.environ["REDIS_URL"])result = client.hscan("my-key", 0)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.HScan(context.Background(), "my-key", 0, "*", 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.hscan("my-key", "0");  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 iter: redis::Iter<(String, String)> = connection.hscan("my-key")?;    for (field, value) in iter {        println!("{field}: {value}");    }    Ok(())}