Nosql Redis在内存不足时做什么？
这可能是一个简单的问题，但我很难找到答案。Redis 2.0如何处理最大分配内存不足的问题？它如何决定删除哪些数据或将哪些数据保留在内存中？Redis与memcached不同，默认情况下（其中Nosql Redis在内存不足时做什么？,nosql,redis,Nosql,Redis,这可能是一个简单的问题，但我很难找到答案。Redis 2.0如何处理最大分配内存不足的问题？它如何决定删除哪些数据或将哪些数据保留在内存中？Redis与memcached不同，默认情况下（其中maxmemory policy参数设置为noeviction），您放入Redis的所有数据都不会被删除，唯一的例外是使用EXPIRE。我最近刚开始阅读有关Redis的文章，所以我不是很肯定。但是，我确实发现了一些可能有用的花边新闻 以下是一段来自： 将Redis用作缓存的另一种方法是 maxmemory指
maxmemory policynoevictionmaxmemorymaxmemorymaxmemorymaxmemory
-在 有过期设置的，正在尝试 删除最近未使用的密钥易失性lru
-在 有过期设置的，正在尝试 取下剩余时间短的钥匙 活着volatile ttl
-删除 在具有 过期设置volatile random
-类似所有键lru
，但将删除每个 钥匙类型，普通钥匙或钥匙 使用过期设置易失性lru
- 类似于volatile random，但将删除 每种钥匙，都是普通钥匙 和具有过期设置的密钥allkeys random
kill-9flushdb# Don't use more memory than 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 cache, or to set
# a hard memory limit for an instance (using the 'noeviction' policy).
#
# WARNING: If you have slaves attached to an instance with maxmemory on,
# the size of the output buffers needed to feed the slaves 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 slaves 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 slaves attached it is suggested that you set a lower
# limit for maxmemory so that there is some free RAM on the system for slave
# output buffers (but this is not needed if the policy is 'noeviction').
#
# maxmemory <bytes>
# MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
# is reached. You can select among five behaviors:
#
# volatile-lru -> remove the key with an expire set using an LRU algorithm
# allkeys-lru -> remove any key according to the LRU algorithm
# volatile-random -> remove a random key 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 expire at all, just return an error on write operations
#
# Note: with any of the above policies, Redis will return an error on write
# operations, when there are no suitable keys for eviction.
#
# At the date of writing these commands are: set setnx setex append
# incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd
# sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby
# zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
# getset mset msetnx exec sort
#
# The default is:
#
# maxmemory-policy volatile-lru
#使用的内存不要超过指定的字节数。
#当达到内存限制时，Redis将尝试删除密钥
#根据选择的逐出策略（请参阅maxmemory策略）。
#
#如果Redis无法根据策略删除密钥，或者如果策略为
#设置为“noeviction”，Redis将开始回复命令错误
#这将使用更多内存，如SET、LPUSH等，并将继续
#回复GET之类的只读命令。
#
#当使用Redis作为LRU缓存或设置
#实例的硬内存限制（使用“noeviction”策略）。
#
#警告：如果将从属服务器连接到maxmemory打开的实例，
#减去馈送从属设备所需的输出缓冲区的大小
#从已用内存计数中删除，以便网络问题/重新同步
#不触发一个循环，其中键被逐出，并依次输出
#从机缓冲区已满，退出的密钥的增量触发删除
#等等，直到数据库完全清空。
#
#简言之。。。如果已连接从属服务器，建议您设置较低的
#限制maxmemory，以便系统上有一些可用RAM供从机使用
#输出缓冲区（但如果策略为“noeviction”，则不需要此缓冲区）。
#
#最大内存
#MAXMEMORY策略：当使用MAXMEMORY时，Redis将如何选择要删除的内容
#到达。您可以从五种行为中进行选择：
#
#volatile lru->使用lru算法删除带有过期集的密钥
#allkeys lru->根据lru算法删除任何密钥
#volatile random->删除带有过期集的随机密钥
#allkeys random->删除随机键，任意键
#volatile ttl->删除过期时间最近的密钥（次要ttl）
#noeviction->根本不过期，只需在写操作中返回一个错误即可
#
#注意：对于上述任何策略，Redis都会在写入时返回错误
#操作，当没有合适的键进行逐出时。
#
#在编写之日，这些命令是：set setnx setex append
#增量说明rpush lpushx lpushx linsert lset RPOPLPPUSH sadd
#烧结店sunion sunionstore sdiff sdiffstore zadd zincrby
#zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
#getset mset msetnx执行排序
#
#默认值为：
#
#maxmemory策略易失性lru
$ redis-cli
127.0.0.1:6379> GET 5
"bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
127.0.0.1:6379> SET 5 a
(error) OOM command not allowed when used memory > 'maxmemory'.
127.0.0.1:6379> MEMORY HELP
1) "MEMORY DOCTOR - Outputs memory problems report"
2) "MEMORY USAGE <key> [SAMPLES <count>] - Estimate memory usage of key"
3) "MEMORY STATS - Show memory usage details"
4) "MEMORY PURGE - Ask the allocator to release memory"
5) "MEMORY MALLOC-STATS - Show allocator internal stats"
127.0.0.1:6379>内存帮助
1） “内存医生-输出内存问题报告”
2） “内存使用情况[示例]-估计密钥的内存使用情况”
3） “内存统计
############################## 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 slaves attached to an instance with maxmemory on,
# the size of the output buffers needed to feed the slaves 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 slaves 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 slaves attached it is suggested that you set a lower
# limit for maxmemory so that there is some free RAM on the system for slave
# output buffers (but this is not needed if the policy is 'noeviction').
#
# maxmemory <bytes>
# MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
# is reached. You can select among five behaviors:
#
# 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.
#
# 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, Redis will return an error on write
# operations, when there are no suitable keys for eviction.
#
# At the date of writing these commands are: set setnx setex append
# incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd
# sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby
# zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby
# getset mset msetnx exec sort
#
# The default is:
#
# maxmemory-policy noeviction
# LRU, LFU and minimal TTL algorithms are not precise algorithms but approximated
# algorithms (in order to save memory), so you can tune it for speed or
# accuracy. For default Redis will check five keys and pick the one that was
# used less recently, you can change the sample size using the following
# configuration directive.
#
# The default of 5 produces good enough results. 10 Approximates very closely
# true LRU but costs more CPU. 3 is faster but not very accurate.
#
# maxmemory-samples 5