redis内存淘汰策略

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redis内存淘汰策略

安装redis

以单机版redis为例，安装redis参考文档：redis单机安装

内存淘汰策略（maxmemory-policy）

启用内存淘汰策略
1. 当设置了 maxmemory（Redis 允许使用的内存上限），内存用满后，Redis 需要"腾空间"时会按以下策略之一淘汰 key
内存淘汰策略
1. noeviction：
  - 不淘汰，写命令（如 SET、LPUSH）直接报错。
  - 适合"不能丢数据，只能报错"的场景。
2. allkeys-lru：
  - 在所有 key 中，淘汰最近最少使用的键（LRU）。
  - 常用于"纯缓存"，非常常见。
3. volatile-lru：
  - 只在有过期时间的 key 集合里按 LRU 淘汰。
  - 没 TTL 的 key 永不淘汰。
4. allkeys-random：
  - 在所有 key 里随机删。
  - 简单粗暴，命中率不可控。
5. volatile-random：
  - 只在有 TTL 的 key 里随机删。
6. volatile-ttl：
  - 只在有 TTL 的 key 中，优先淘汰剩余生存时间最短的 key。
7. allkeys-lfu：
  - 在所有 key 中，淘汰访问频率最低的键（LFU）。
  - 比 LRU 更关注"长期热度"。
8. volatile-lfu：
  - 只在有 TTL 的 key 里按 LFU 淘汰。
内存淘汰策略选择
1. 纯缓存场景（推荐最多）
  - 策略：allkeys-lru 或新版本的 allkeys-lfu
  - 理由：所有数据都可丢，优先保留"近期/高频访问"的 key，命中率最好。
2. 只有部分 key 允许被淘汰（缓存 + 持久数据混用）
  - 策略：volatile-lru / volatile-lfu / volatile-ttl，这些策略只关注有TTL的key
  - 做法：
    - 给"可淘汰的缓存 key"设置 TTL
    - 不可丢的数据不设置 TTL，这样只会淘汰带过期的缓存 key。
3. 严格不能丢写入（少见，一般配合持久化存储）
  - 策略：noeviction
  - 效果：内存打满时，写请求报错而不是删数据，多用于"Redis 不做缓存、只做强一致存储"的特殊场景。

配置内存淘汰策略

在配置文件redis.conf中配置，改完后重启 Redis 生效。（maxmemory单位支持 kb/mb/gb/字节数）

properties 复制代码

############################## MEMORY MANAGEMENT ################################

# Set a memory usage limit to the specified amount of bytes.
# When the memory limit is reached Redis will try to remove keys
# according to the eviction policy selected (see maxmemory-policy).
#
# If Redis can't remove keys according to the policy, or if the policy is
# set to 'noeviction', Redis will start to reply with errors to commands
# that would use more memory, like SET, LPUSH, and so on, and will continue
# to reply to read-only commands like GET.
#
# This option is usually useful when using Redis as an LRU or LFU cache, or to
# set a hard memory limit for an instance (using the 'noeviction' policy).
#
# WARNING: If you have replicas attached to an instance with maxmemory on,
# the size of the output buffers needed to feed the replicas are subtracted
# from the used memory count, so that network problems / resyncs will
# not trigger a loop where keys are evicted, and in turn the output
# buffer of replicas is full with DELs of keys evicted triggering the deletion
# of more keys, and so forth until the database is completely emptied.
#
# In short... if you have replicas attached it is suggested that you set a lower
# limit for maxmemory so that there is some free RAM on the system for replica
# output buffers (but this is not needed if the policy is 'noeviction').
#
# maxmemory <bytes>
maxmemory 1gb


# MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
# is reached. You can select one from the following behaviors:
#
# volatile-lru -> Evict using approximated LRU, only keys with an expire set.
# allkeys-lru -> Evict any key using approximated LRU.
# volatile-lfu -> Evict using approximated LFU, only keys with an expire set.
# allkeys-lfu -> Evict any key using approximated LFU.
# volatile-random -> Remove a random key having an expire set.
# allkeys-random -> Remove a random key, any key.
# volatile-ttl -> Remove the key with the nearest expire time (minor TTL)
# noeviction -> Don't evict anything, just return an error on write operations.
#
# LRU means Least Recently Used
# LFU means Least Frequently Used
#
# Both LRU, LFU and volatile-ttl are implemented using approximated
# randomized algorithms.
#
# Note: with any of the above policies, when there are no suitable keys for
# eviction, Redis will return an error on write operations that require
# more memory. These are usually commands that create new keys, add data or
# modify existing keys. A few examples are: SET, INCR, HSET, LPUSH, SUNIONSTORE,
# SORT (due to the STORE argument), and EXEC (if the transaction includes any
# command that requires memory).
#
# The default is:
#
# maxmemory-policy noeviction
maxmemory-policy allkeys-lru

在 redis-cli 中执行，立刻生效，但重启后会丢失（除非同时改了 redis.conf）。（maxmemory单位支持 kb/mb/gb/字节数）
shell 复制代码
```
CONFIG SET maxmemory 1gb
CONFIG SET maxmemory-policy allkeys-lru
```

参考资料

https://www.bilibili.com/video/BV13R4y1v7sP

注意事项

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redis内存淘汰策略

redis内存淘汰策略

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redis内存淘汰策略

安装redis

内存淘汰策略（maxmemory-policy）

参考资料

注意事项