Memory Limits and Eviction

Setting a memory limit

maxmemory caps Redis memory usage. When the limit is reached, Redis applies the eviction policy to decide which keys to remove. You can set it in redis.conf or at runtime with CONFIG SET.

maxmemory 512mb
maxmemory-policy allkeys-lru

Eviction policies

Policy	Behavior
noeviction	Return error on writes when full (default; safe for databases)
allkeys-lru	Evict least recently used key from all keys
volatile-lru	Evict LRU from keys with a TTL set
allkeys-lfu	Evict least frequently used key from all keys
volatile-lfu	Evict LFU from keys with a TTL
volatile-ttl	Evict the key with the shortest remaining TTL
allkeys-random	Evict a random key from all keys
volatile-random	Evict a random key from keys with a TTL

Checking and changing policy at runtime

127.0.0.1:6379> CONFIG GET maxmemory-policy
1) "maxmemory-policy"
2) "noeviction"
127.0.0.1:6379> CONFIG SET maxmemory-policy allkeys-lru
OK
127.0.0.1:6379> CONFIG GET maxmemory
1) "maxmemory"
2) "0"
127.0.0.1:6379> CONFIG SET maxmemory 256mb
OK

CONFIG GET maxmemory-policy
CONFIG SET maxmemory-policy allkeys-lru
CONFIG GET maxmemory
CONFIG SET maxmemory 256mb

Copy commands ⧉

🟥 Cache vs database — choose the right policy

As a cache, set maxmemory plus an allkeys-lru or allkeys-lfu policy so Redis automatically removes the least useful keys. As a primary database, use noeviction so writes fail loudly rather than silently dropping data.

Which eviction policy evicts the least recently used key from ALL keys?

volatile-lru allkeys-lru allkeys-lfu volatile-ttl

What is the default eviction policy in Redis?

allkeys-lru volatile-lru noeviction allkeys-random

The `volatile-ttl` policy evicts keys based on what criterion?

Least recently used among all keys A random selection from all keys The shortest remaining TTL among keys that have a TTL set Least frequently used among all keys

Which command sets the eviction policy at runtime?

CONFIG SET maxmemory-policy SET maxmemory-policy CONFIG UPDATE eviction POLICY SET eviction

Submit

Mark as complete