Redis Sorted Set: Pagination (Detailed Guide w/ Code Examples)

Use Case(s)

• Displaying a page of results from a leaderboard.
• Fetching paginated data for infinite scroll in an application.
• Implementing paging through search results with scores.

Code Examples

Python

import redis

client = redis.StrictRedis(host='localhost', port=6379, db=0)

# Add elements to the sorted set
client.zadd('myset', {'member1': 1, 'member2': 2, 'member3': 3, 'member4': 4})

# Paginate with start and end index
start = 0
end = 2
results = client.zrange('myset', start, end, withscores=True)
print(results)

Node.js

const redis = require("redis");
const client = redis.createClient();

client.on("error", function (error) {
  console.error(error);
});

client.zadd("myset", 1, "member1", 2, "member2", 3, "member3", 4, "member4");

// Paginate with start and end index
const start = 0;
const end = 2;

client.zrange("myset", start, end, "WITHSCORES", (err, result) => {
  if (err) throw err;
  console.log(result);
});

Golang

package main

import (
	"fmt"
	"github.com/go-redis/redis/v8"
	"context"
)

func main() {
	ctx := context.Background()
	client := redis.NewClient(&redis.Options{
		Addr: "localhost:6379",
	})

	// Add elements to the sorted set
	client.ZAdd(ctx, "myset", &redis.Z{Score: 1, Member: "member1"})
	client.ZAdd(ctx, "myset", &redis.Z{Score: 2, Member: "member2"})
	client.ZAdd(ctx, "myset", &redis.Z{Score: 3, Member: "member3"})
	client.ZAdd(ctx, "myset", &redis.Z{Score: 4, Member: "member4"})

	// Paginate with start and end index
	start := int64(0)
	end := int64(2)
	results, err := client.ZRangeWithScores(ctx, "myset", start, end).Result()
	if err != nil {
		panic(err)
	}

	for _, z := range results {
		fmt.Printf("%v: %f\n", z.Member, z.Score)
	}
}

Best Practices

• Ensure indices used for pagination are properly calculated to avoid off-by-one errors.
• Consider using ZREVRANGE if you need descending order pagination.
• Use ZRANGEBYSCORE with LIMIT for more controlled pagination based on scores rather than indices.

Common Mistakes

• Forgetting to include the WITHSCORES option when needed, which can lead to confusion with results.
• Using zero-based indexing incorrectly can lead to skipped or duplicated entries in pages.
• Not handling empty results correctly, which may occur at the boundaries of the dataset.

FAQs

Q: How do I handle large datasets efficiently with Redis sorted sets? A: Use cursor-based pagination with ZSCAN to avoid loading too many elements into memory at once.

Q: Can I delete a range of elements while paginating? A: Yes, use ZREMRANGEBYRANK to remove elements by their rank range.