Redis maxclients Explained: Configuring Maximum Client Connections

Introduction

The maxclients directive controls the maximum number of client connections that a Redis server can accept simultaneously.

Each client connection consumes system resources, including memory and file descriptors. Without a connection limit, excessive client connections may overwhelm the server and reduce overall performance.

This guide explains how maxclients works, how to configure it, common connection limit issues, and best practices for production environments.

Default Value

Most Redis installations use:

maxclients 10000

Redis can accept up to 10,000 concurrent client connections by default.

The actual limit may be lower if the operating system does not provide enough file descriptors.

Syntax

maxclients

Examples:

maxclients 5000

maxclients 20000

How maxclients Works

When the number of connected clients reaches the configured limit:

Existing clients continue to operate normally.

New connection attempts are rejected.

Clients attempting to connect may receive an error similar to:

ERR max number of clients reached

Configure maxclients

Open the Redis configuration file.

sudo nano /etc/redis.conf

Locate:

maxclients 10000

Modify it if necessary.

Example:

maxclients 20000

Restart Redis.

sudo systemctl restart redis

Verify the Configuration

Run:

redis-cli CONFIG GET maxclients

Example output:

1) "maxclients"

2) "20000"

Check Current Connections

Redis provides client statistics.

Run:

redis-cli INFO clients

Example output:

connected_clients:125

blocked_clients:0

To list connected clients:

redis-cli CLIENT LIST

Operating System Limits

The maxclients setting is also affected by the operating system's file descriptor limit.

Check the current limit:

ulimit -n

Example:

1024

If the operating system allows only 1,024 file descriptors, Redis cannot support 10,000 client connections.

Increase the file descriptor limit before raising maxclients.

Choosing the Right Value

The appropriate setting depends on your workload.

| Environment              | Suggested Value |
| ------------------------ | --------------- |
| Development              | 100–500         |
| Small web application    | 1,000–5,000     |
| Medium production server | 10,000          |
| Large production server  | 20,000–50,000   |

Higher values require more memory and operating system resources.

Common Mistakes

Increasing maxclients Without Raising ulimit

Redis cannot exceed the operating system's file descriptor limit.

Both settings must be configured together.

Assuming More Connections Improve Performance

A higher connection limit does not automatically make Redis faster.

Excessive connections may increase memory consumption and scheduling overhead.

Ignoring Connection Leaks

Applications that fail to close unused connections may eventually reach the client limit.

Use connection pooling whenever possible.

Best Practices

Monitor the number of connected clients regularly.

Use connection pools in application frameworks.

Increase the operating system's file descriptor limit before raising maxclients.

Avoid unnecessarily large connection limits.

Investigate connection leaks if client counts continue to grow.

Related Articles

Redis Explained

Redis timeout Explained

Redis tcp-keepalive Explained

Redis protected-mode Explained

Redis bind Explained

Conclusion

The maxclients directive limits the number of simultaneous client connections that Redis accepts, helping protect the server from resource exhaustion. Choosing an appropriate value ensures that Redis can handle expected workloads while maintaining stable performance.

When increasing maxclients, remember that the operating system's file descriptor limit must also be adjusted. Monitoring client connections and using connection pooling are essential practices for reliable production deployments.