今天来聊聊Redis的过期策略和内存淘汰策略最全总结与分析

# volatile-lru -> Evict using approximated LRU among the keys with an expire set.
# allkeys-lru -> Evict any key using approximated LRU.
# volatile-lfu -> Evict using approximated LFU among the keys with an expire set.
# allkeys-lfu -> Evict any key using approximated LFU.
# volatile-random -> Remove a random key among the ones with 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.

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volatile-lru：当内存不足以容纳新写入数据时，在设置了过期时间的键空间中，移除最近最少使用的key。

allkeys-lru：当内存不足以容纳新写入数据时，在键空间中，移除最近最少使用的key（这个是最常用的）。

volatile-lfu：当内存不足以容纳新写入数据时，在过期密集的键中，使用LFU算法进行删除key。

allkeys-lfu：当内存不足以容纳新写入数据时，使用LFU算法移除所有的key。

volatile-random：当内存不足以容纳新写入数据时，在设置了过期的键中，随机删除一个key。

allkeys-random：当内存不足以容纳新写入数据时，随机删除一个或者多个key。

volatile-ttl：当内存不足以容纳新写入数据时，在设置了过期时间的键空间中，有更早过期时间的key优先移除。

noeviction：当内存不足以容纳新写入数据时，新写入操作会报错。

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# Set a memory usage limit to the specified amount of bytes.
#将内存使用限制设置为指定的字节数。
# When the memory limit is reached Redis will try to remove keys
#当达到内存限制时，Redis将尝试删除密钥
# according to the eviction policy selected (see maxmemory-policy).
#根据所选的逐出策略（请参阅maxmemory策略）。
#
#
# If Redis can't remove keys according to the policy, or if the policy is
#如果Redis不能根据策略删除密钥，或者如果策略是
# set to 'noeviction', Redis will start to reply with errors to commands
#设置为“noeviction”时，Redis将开始对命令进行错误的应答
# that would use more memory, like SET, LPUSH, and so on, and will continue
#这将使用更多内存，如SET、LPUSH等，并将继续
# to reply to read-only commands like GET.
#回复像GET这样的只读命令。
#
#
# This option is usually useful when using Redis as an LRU or LFU cache, or to
#当将Redis用作LRU或LFU缓存或
# set a hard memory limit for an instance (using the 'noeviction' policy).
#为实例设置硬内存限制（使用“noeviction”策略）。
#
#
# WARNING: If you have replicas attached to an instance with maxmemory on,
#警告：如果将副本附加到启用了maxmemory的实例，
# the size of the output buffers needed to feed the replicas are subtracted
#减去为复制副本提供数据所需的输出缓冲区的大小
# from the used memory count, so that network problems / resyncs will
#从网络中重新同步使用的问题
# not trigger a loop where keys are evicted, and in turn the output
#不触发一个循环，其中键被逐出，而反过来输出
# buffer of replicas is full with DELs of keys evicted triggering the deletion
#复制副本的缓冲区已满，退出的密钥将触发删除
# of more keys, and so forth until the database is completely emptied.
#直到数据库完全清空。
#
# In short... if you have replicas attached it is suggested that you set a lower
#简而言之。。。如果您附加了副本，建议您设置较低的
# limit for maxmemory so that there is some free RAM on the system for replica
#限制maxmemory，以便系统上有一些可用的RAM用于复制
# output buffers (but this is not needed if the policy is 'noeviction').
#输出缓冲区（但如果策略为“noeviction”，则不需要此缓冲区）。
# maxmemory <bytes>
#最大内存<字节>
# MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
#MAXMEMORY策略：当MAXMEMORY时Redis如何选择要删除的内容
# is reached. You can select among five behaviors:
#已到达。您可以从五种行为中进行选择：
#
# volatile-lru -> Evict using approximated LRU among the keys with an expire set.
#volatile lru->在具有expire集的密钥中使用近似的lru进行逐出。
# allkeys-lru -> Evict any key using approximated LRU.
#allkeys lru->使用近似的lru逐出任何键。
# volatile-lfu -> Evict using approximated LFU among the keys with an expire set.
#volatile lfu->在具有expire集的密钥中使用近似的lfu进行逐出。
# allkeys-lfu -> Evict any key using approximated LFU.
#allkeys lfu->使用近似的lfu逐出任何键。
# volatile-random -> Remove a random key among the ones with an expire set.
#volatile random->从具有expire集的密钥中删除一个随机密钥。
# allkeys-random -> Remove a random key, any key.
#allkeys random->移除一个随机键，任意键。
# volatile-ttl -> Remove the key with the nearest expire time (minor TTL)
#volatile ttl->删除最接近过期时间的密钥（minor ttl）
# noeviction -> Don't evict anything, just return an error on write operations.
#noeviction->不要逐出任何内容，只要在写操作时返回一个错误。
# LRU means Least Recently Used
#LRU表示最近最少使用
# LFU means Least Frequently Used
#LFU表示使用频率最低
# Both LRU, LFU and volatile-ttl are implemented using approximated
#LRU、LFU和volatile ttl都是用近似方法实现的
# randomized algorithms.
#随机算法。
# Note: with any of the above policies, Redis will return an error on write
#注意：如果使用上述任何策略，Redis将在写入时返回错误
#       operations, when there are no suitable keys for eviction.
#操作，当没有合适的钥匙驱逐。
#
#At the date of writing these commands are: set setnx setex append
#在编写这些命令的日期是：set setnx setex append
#incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd
#增加/减少脉冲低压脉冲rpushx lpushx linsert lset RPOPPLPUSH sadd
#sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby
#sinter sinterstore sunion sunionstore sdiffstore zadd zincrby
#zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
#zunionstore zinterstore hset hsetnx hmset hincrby incrby递减
#getset mset msetnx exec sort
#getset mset msetnx exec排序
#
#
# The default is:
#默认值为：
#
#
# maxmemory-policy noeviction
#maxmemory策略不可用
# LRU, LFU and minimal TTL algorithms are not precise algorithms but approximated
#LRU、LFU和最小TTL算法不是精确算法而是近似算法
# algorithms (in order to save memory), so you can tune it for speed or
#算法（为了节省内存），所以你可以调整它的速度或
# accuracy. For default Redis will check five keys and pick the one that was
#准确度。对于默认的Redis将检查五个键并选择一个
# used less recently, you can change the sample size using the following
#最近使用较少，可以使用以下命令更改样本大小
# configuration directive.
#配置指令。
#
#
# The default of 5 produces good enough results. 10 Approximates very closely
#默认值为5会产生足够好的结果。10非常接近
# true LRU but costs more CPU. 3 is faster but not very accurate.
#真正的外场可更换单元，但占用更多的CPU。3更快，但不是很准确。
# maxmemory-samples 5
#maxmemory示例5
# Starting from Redis 5, by default a replica will ignore its maxmemory setting
#从Redis 5开始，默认情况下副本将忽略其maxmemory设置
# (unless it is promoted to master after a failover or manually). It means
#（除非在故障转移后或手动升级为主节点）。意思是
# that the eviction of keys will be just handled by the master, sending the
#密钥的收回将由主机处理，发送
# DEL commands to the replica as keys evict in the master side.
#DEL命令在主服务器端作为密钥收回。
#
# This behavior ensures that masters and replicas stay consistent, and is usually
#这种行为可以确保主机和副本保持一致，并且通常
# what you want, however if your replica is writable, or you want the replica to have
#但是，如果您的复制副本是可写的，或者您希望复制副本具有
# a different memory setting, and you are sure all the writes performed to the
#不同的内存设置，并且您确定对
# replica are idempotent, then you may change this default (but be sure to understand
#复制副本是幂等的，那么您可以更改这个默认值（但是一定要理解
# what you are doing).
#你在做什么）。
#
# Note that since the replica by default does not evict, it may end using more
#请注意，由于复制副本在默认情况下不会逐出，它可能会使用更多
# memory than the one set via maxmemory (there are certain buffers that may
#内存大于通过maxmemory设置的内存（有某些缓冲区可能
# be larger on the replica, or data structures may sometimes take more memory and so
#复制副本越大，或者数据结构有时可能占用更多内存，因此
# forth). So make sure you monitor your replicas and make sure they have enough
#第四）。所以一定要监控你的复制品，确保它们有足够的
# memory to never hit a real out-of-memory condition before the master hits
#内存在主机命中之前永远不会遇到内存不足的情况
# the configured maxmemory setting.
#配置的maxmemory设置。
#
#
# replica-ignore-maxmemory yes
#复制副本忽略maxmemory是

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