LLEN

Get the length of a list

Overview

Returns the length of the list stored at key. If key does not exist, it is interpreted as an empty list and 0 is returned.

Method Signature

llen(key: string): Promise<number>

Parameters

key · string · required

The key of the list.

Return Value

length · number

The length of the list. Returns 0 if the list does not exist.

Examples

Basic Usage

import { Redis } from '@upstash/redis';

const redis = new Redis({
  url: process.env.UPSTASH_REDIS_REST_URL,
  token: process.env.UPSTASH_REDIS_REST_TOKEN,
});

// Add some elements
await redis.rpush('mylist', 'one', 'two', 'three');

// Get the length
const length = await redis.llen('mylist');
console.log(length); // 3

// Check non-existent list
const emptyLength = await redis.llen('nonexistent');
console.log(emptyLength); // 0

Queue Size Monitoring

// Check queue size before processing
const queueSize = await redis.llen('queue:jobs');

if (queueSize > 100) {
  console.log('Queue is getting long, consider scaling up workers');
}

if (queueSize === 0) {
  console.log('No jobs to process');
}

Tracking List Growth

// Monitor list size over time
const initialSize = await redis.llen('events');

// Add new events
await redis.rpush('events', 'event1', 'event2', 'event3');

const newSize = await redis.llen('events');
const added = newSize - initialSize;
console.log(`Added ${added} new events`);

Conditional Operations

// Only add items if list is below a certain size
const maxSize = 1000;
const currentSize = await redis.llen('limited:list');

if (currentSize < maxSize) {
  await redis.rpush('limited:list', 'new-item');
} else {
  console.log('List is full, cannot add more items');
}

Pagination Info

const pageSize = 10;
const totalItems = await redis.llen('items');
const totalPages = Math.ceil(totalItems / pageSize);

console.log(`Total items: ${totalItems}`);
console.log(`Total pages: ${totalPages}`);

Health Check

// Check if critical queues are empty
const criticalQueues = ['queue:high-priority', 'queue:normal', 'queue:low'];

for (const queue of criticalQueues) {
  const size = await redis.llen(queue);
  console.log(`${queue}: ${size} items`);
}

Rate Limiting Check

// Check if user has exceeded rate limit
const userKey = `rate:user:${userId}`;
const requestCount = await redis.llen(userKey);

if (requestCount > 100) {
  throw new Error('Rate limit exceeded');
}

await redis.rpush(userKey, Date.now().toString());

See Also

• LRANGE - Get a range of elements from a list
• LPUSH - Insert elements at the head of a list
• RPUSH - Insert elements at the tail of a list
• LPOP - Remove and return the first element of a list