Redis - Max Memory & Key Eviction Policy

Introduction

To ensure that Redis does not exceed the maximum amount of physical memory, several so-called key eviction policies are available. These policies allow stored keys to be automatically removed based on criteria defined by the policy until the memory limit is no longer exceeded.

Prerequisites

• Redis server (with root access)

Customize the Configuration

Connect to your Redis server, for example via SSH, and log in as the SSH root user.

Open the Redis configuration file with an editor of your choice; in this case, we’ll use nano:

nano /etc/redis/redis.conf 

systemctl restart redis-server.service

Max Memory

The maxmemory setting allows you to limit the amount of memory used by Redis. Search the configuration file for maxmemory and set the desired value.

maxmemory 4GB # sets the limit to 4 GiB

The following table shows the possible values for the maximum memory size:

Difference Between LRU & LFU

What is LRU (Least Recently Used)?

LRU is an algorithm for memory and cache optimization that always removes the data that has not been used for the longest time. This means that when memory is full, the system first deletes the entries that were most recently used the least frequently.\nLRU is particularly well-suited for applications where current data is significantly more important than older data, as it realistically reflects typical user behavior.

What is LFU (Least Frequently Used)?

LFU is an algorithm for efficient cache management that removes the entries that have been used the least overall. Instead of focusing on the time of the last use, LFU counts how often a key has been accessed.\nLFU is ideal when frequently used data should remain in the cache and rarely used data should be systematically evicted.

Quick Comparison: LRU vs. LFU

• LRU prioritizes recency
• LFU prioritizes frequency of use

Both methods improve cache performance but follow different strategies for memory optimization.

Max Memory Policy

The Max Memory Policy setting defines Redis’s eviction behavior when adding records would cause the Max Memory Limit to be exceeded.

Search the configuration file for maxmemory-policy and set the desired key eviction policy.

maxmemory-policy volatile-ttl # default setting

Key Eviction Policies

The following table summarizes all key eviction policies supported by Redis and their descriptions.

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