Redis

Redis是一个单线程 + Epoll + 计算向数据移动的内存型数据库。

常用命令

常见命令文档、Redis命令参考手册完整版

redis-cli -h host -p port -a password

命令 描述
SELECT 切换数据库
Dbsize 查看当前数据库的key的数量
Flushdb 清空当前库
Flushall 通杀全部库 
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127.0.0.1:6379> help @generic

DEL key [key ...]
summary: Delete a key
since: 1.0.0

DUMP key
summary: Return a serialized version of the value stored at the specified key.
since: 2.6.0

EXISTS key [key ...]
summary: Determine if a key exists
since: 1.0.0

EXPIRE key seconds
summary: Set a key's time to live in seconds
since: 1.0.0

EXPIREAT key timestamp
summary: Set the expiration for a key as a UNIX timestamp
since: 1.2.0

KEYS pattern
summary: Find all keys matching the given pattern
since: 1.0.0

MIGRATE host port key| destination-db timeout [COPY] [REPLACE] [KEYS key]
summary: Atomically transfer a key from a Redis instance to another one.
since: 2.6.0

MOVE key db
summary: Move a key to another database
since: 1.0.0

OBJECT subcommand [arguments [arguments ...]]
summary: Inspect the internals of Redis objects
since: 2.2.3

PERSIST key
summary: Remove the expiration from a key
since: 2.2.0

PEXPIRE key milliseconds
summary: Set a key's time to live in milliseconds
since: 2.6.0

PEXPIREAT key milliseconds-timestamp
summary: Set the expiration for a key as a UNIX timestamp specified in milliseconds
since: 2.6.0

PTTL key
summary: Get the time to live for a key in milliseconds
since: 2.6.0

RANDOMKEY -
summary: Return a random key from the keyspace
since: 1.0.0

RENAME key newkey
summary: Rename a key
since: 1.0.0

RENAMENX key newkey
summary: Rename a key, only if the new key does not exist
since: 1.0.0

RESTORE key ttl serialized-value [REPLACE]
summary: Create a key using the provided serialized value, previously obtained using DUMP.
since: 2.6.0

SCAN cursor [MATCH pattern] [COUNT count]
summary: Incrementally iterate the keys space
since: 2.8.0

SORT key [BY pattern] [LIMIT offset count] [GET pattern [GET pattern ...]] [ASC|DESC] [ALPHA] [STORE destination]
summary: Sort the elements in a list, set or sorted set
since: 1.0.0

TOUCH key [key ...]
summary: Alters the last access time of a key(s). Returns the number of existing keys specified.
since: 3.2.1

TTL key
summary: Get the time to live for a key
since: 1.0.0

TYPE key
summary: Determine the type stored at key
since: 1.0.0

UNLINK key [key ...]
summary: Delete a key asynchronously in another thread. Otherwise it is just as DEL, but non blocking.
since: 4.0.0

WAIT numreplicas timeout
summary: Wait for the synchronous replication of all the write commands sent in the context of the current connection
since: 3.0.0

POST ...options...
summary: Help not available
since: not known

SUBSTR key arg arg 
summary: Help not available
since: not known

RESTORE-ASKING key arg arg ...options...
summary: Help not available
since: not known

HOST: ...options...
summary: Help not available
since: not known

PFDEBUG arg arg ...options...
summary: Help not available
since: not known

MODULE arg ...options...
summary: Help not available
since: not known

GEORADIUSBYMEMBER_RO key arg arg arg ...options...
summary: Help not available
since: not known

XSETID key arg 
summary: Help not available
since: not known

GEORADIUS_RO key arg arg arg arg ...options...
summary: Help not available
since: not known

ASKING 
summary: Help not available
since: not known

PSYNC arg arg 
summary: Help not available
since: not known

REPLCONF ...options...
summary: Help not available
since: not known

LATENCY arg ...options...
summary: Help not available
since: not known

PFSELFTEST 
summary: Help not available
since: not known

LOLWUT ...options...
summary: Help not available
since: not known

String

字符串有正向索引和反向索引，正向开头index=0开始，反向末尾index=-1开始。

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127.0.0.1:6379> help @String

APPEND key value
summary: Append a value to a key
since: 2.0.0

DECR key
summary: Decrement the integer value of a key by one
since: 1.0.0

DECRBY key decrement
summary: Decrement the integer value of a key by the given number
since: 1.0.0

GET key
summary: Get the value of a key
since: 1.0.0

GETRANGE key start end
summary: Get a substring of the string stored at a key
since: 2.4.0

GETSET key value
summary: Set the string value of a key and return its old value
since: 1.0.0

INCR key
summary: Increment the integer value of a key by one
since: 1.0.0

INCRBY key increment
summary: Increment the integer value of a key by the given amount
since: 1.0.0

INCRBYFLOAT key increment
summary: Increment the float value of a key by the given amount
since: 2.6.0

MGET key [key ...]
summary: Get the values of all the given keys
since: 1.0.0

MSET key value [key value ...]
summary: Set multiple keys to multiple values
since: 1.0.1

MSETNX key value [key value ...]
summary: Set multiple keys to multiple values, only if none of the keys exist
since: 1.0.1

PSETEX key milliseconds value
summary: Set the value and expiration in milliseconds of a key
since: 2.6.0

SET key value [expiration EX seconds|PX milliseconds] [NX|XX]
summary: Set the string value of a key
since: 1.0.0

SETEX key seconds value
summary: Set the value and expiration of a key
since: 2.0.0

SETNX key value
summary: Set the value of a key, only if the key does not exist
since: 1.0.0

SETRANGE key offset value
summary: Overwrite part of a string at key starting at the specified offset
since: 2.2.0

STRLEN key
summary: Get the length of the value stored in a key
since: 2.2.0
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Incr等数值命令适用场景：
抢购，秒杀，详情页，点赞，评论
规避并发下，对数据库的事务操作，完全由redis内存操作代替

BitMap

对二进制的Index位数进行设置值

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BITCOUNT key [start end]
summary: Count set bits in a string
since: 2.6.0

BITFIELD key [GET type offset] [SET type offset value] [INCRBY type offset increment] [OVERFLOW WRAP|SAT|FAIL]
summary: Perform arbitrary bitfield integer operations on strings
since: 3.2.0

BITOP operation destkey key [key ...]
summary: Perform bitwise operations between strings
since: 2.6.0

BITPOS key bit [start] [end]
summary: Find first bit set or clear in a string
since: 2.8.7

SETBIT key offset value
summary: Sets or clears the bit at offset in the string value stored at key
since: 2.2.0

GETBIT key offset
summary: Returns the bit value at offset in the string value stored at key
since: 2.2.0
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案例：
setbit k1 1 1               0100 0000=@
setbit k1 7 1				0100 0001=A
setbit k1 9 1				0100 0001 0100 0000=A@

默认会转换成字符集  ascii 输出
其他一般叫做扩展字符集
扩展：  其他字符集不在对ascii重编码


redis的位操作适用场景：
1.有用户系统，统计用户登录天数，且窗口随机,每个用户有366位数据，一天一个，用BITCOUNT算出多少天
setbit sean 1 1
setbit sean 7 1
setbit sean 364 1
STRLEN sean
BITCOUNT sean -2 -1

2.活跃用户统计！随即窗口,多少用户多少个bit，一天一个key，数据与运算后使用BITCOUNT
setbit 20190101   1  1
setbit 20190102   1  1
setbit 20190102   7  1
bitop  or   destkey 20190101  20190102
BITCOUNT  destkey  0 -1

Hash

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127.0.0.1:6379> help @hash

HDEL key field [field ...]
summary: Delete one or more hash fields
since: 2.0.0

HEXISTS key field
summary: Determine if a hash field exists
since: 2.0.0

HGET key field
summary: Get the value of a hash field
since: 2.0.0

HGETALL key
summary: Get all the fields and values in a hash
since: 2.0.0

HINCRBY key field increment
summary: Increment the integer value of a hash field by the given number
since: 2.0.0

HINCRBYFLOAT key field increment
summary: Increment the float value of a hash field by the given amount
since: 2.6.0

HKEYS key
summary: Get all the fields in a hash
since: 2.0.0

HLEN key
summary: Get the number of fields in a hash
since: 2.0.0

HMGET key field [field ...]
summary: Get the values of all the given hash fields
since: 2.0.0

HMSET key field value [field value ...]
summary: Set multiple hash fields to multiple values
since: 2.0.0

HSCAN key cursor [MATCH pattern] [COUNT count]
summary: Incrementally iterate hash fields and associated values
since: 2.8.0

HSET key field value
summary: Set the string value of a hash field
since: 2.0.0

HSETNX key field value
summary: Set the value of a hash field, only if the field does not exist
since: 2.0.0

HSTRLEN key field
summary: Get the length of the value of a hash field
since: 3.2.0

HVALS key
summary: Get all the values in a hash
since: 2.0.0

List

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127.0.0.1:6379> help @list

BLPOP key [key ...] timeout
summary: Remove and get the first element in a list, or block until one is available
since: 2.0.0

BRPOP key [key ...] timeout
summary: Remove and get the last element in a list, or block until one is available
since: 2.0.0

BRPOPLPUSH source destination timeout
summary: Pop a value from a list, push it to another list and return it; or block until one is available
since: 2.2.0

LINDEX key index
summary: Get an element from a list by its index
since: 1.0.0

LINSERT key BEFORE|AFTER pivot value
summary: Insert an element before or after another element in a list
since: 2.2.0

LLEN key
summary: Get the length of a list
since: 1.0.0

LPOP key
summary: Remove and get the first element in a list
since: 1.0.0

LPUSH key value [value ...]
summary: Prepend one or multiple values to a list
since: 1.0.0

LPUSHX key value
summary: Prepend a value to a list, only if the list exists
since: 2.2.0

LRANGE key start stop
summary: Get a range of elements from a list
since: 1.0.0

LREM key count value
summary: Remove elements from a list
since: 1.0.0

LSET key index value
summary: Set the value of an element in a list by its index
since: 1.0.0

LTRIM key start stop
summary: Trim a list to the specified range
since: 1.0.0

RPOP key
summary: Remove and get the last element in a list
since: 1.0.0

RPOPLPUSH source destination
summary: Remove the last element in a list, prepend it to another list and return it
since: 1.2.0

RPUSH key value [value ...]
summary: Append one or multiple values to a list
since: 1.0.0

RPUSHX key value
summary: Append a value to a list, only if the list exists
since: 2.2.0

Set

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127.0.0.1:6379> help @set

SADD key member [member ...]
summary: Add one or more members to a set
since: 1.0.0

SCARD key
summary: Get the number of members in a set
since: 1.0.0

SDIFF key [key ...]
summary: Subtract multiple sets
since: 1.0.0

SDIFFSTORE destination key [key ...]
summary: Subtract multiple sets and store the resulting set in a key
since: 1.0.0

SINTER key [key ...]
summary: Intersect multiple sets
since: 1.0.0

SINTERSTORE destination key [key ...]
summary: Intersect multiple sets and store the resulting set in a key
since: 1.0.0

SISMEMBER key member
summary: Determine if a given value is a member of a set
since: 1.0.0

SMEMBERS key
summary: Get all the members in a set
since: 1.0.0

SMOVE source destination member
summary: Move a member from one set to another
since: 1.0.0

SPOP key [count]
summary: Remove and return one or multiple random members from a set
since: 1.0.0

SRANDMEMBER key [count]
summary: Get one or multiple random members from a set
since: 1.0.0

SREM key member [member ...]
summary: Remove one or more members from a set
since: 1.0.0

SSCAN key cursor [MATCH pattern] [COUNT count]
summary: Incrementally iterate Set elements
since: 2.8.0

SUNION key [key ...]
summary: Add multiple sets
since: 1.0.0

SUNIONSTORE destination key [key ...]
summary: Add multiple sets and store the resulting set in a key
since: 1.0.0
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特性：
【无序】&&【随机性】&&【去重】
放入的多少不同，元素存储的顺序不同。

Sorted_set

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127.0.0.1:6379> help @sorted_set

BZPOPMAX key [key ...] timeout
summary: Remove and return the member with the highest score from one or more sorted sets, or block until one is available
since: 5.0.0

BZPOPMIN key [key ...] timeout
summary: Remove and return the member with the lowest score from one or more sorted sets, or block until one is available
since: 5.0.0

ZADD key [NX|XX] [CH] [INCR] score member [score member ...]
summary: Add one or more members to a sorted set, or update its score if it already exists
since: 1.2.0

ZCARD key
summary: Get the number of members in a sorted set
since: 1.2.0

ZCOUNT key min max
summary: Count the members in a sorted set with scores within the given values
since: 2.0.0

ZINCRBY key increment member
summary: Increment the score of a member in a sorted set
since: 1.2.0

ZINTERSTORE destination numkeys key [key ...] [WEIGHTS weight] [AGGREGATE SUM|MIN|MAX]
summary: Intersect multiple sorted sets and store the resulting sorted set in a new key
since: 2.0.0

ZLEXCOUNT key min max
summary: Count the number of members in a sorted set between a given lexicographical range
since: 2.8.9

ZPOPMAX key [count]
summary: Remove and return members with the highest scores in a sorted set
since: 5.0.0

ZPOPMIN key [count]
summary: Remove and return members with the lowest scores in a sorted set
since: 5.0.0

ZRANGE key start stop [WITHSCORES]
summary: Return a range of members in a sorted set, by index
since: 1.2.0

ZRANGEBYLEX key min max [LIMIT offset count]
summary: Return a range of members in a sorted set, by lexicographical range
since: 2.8.9

ZRANGEBYSCORE key min max [WITHSCORES] [LIMIT offset count]
summary: Return a range of members in a sorted set, by score
since: 1.0.5

ZRANK key member
summary: Determine the index of a member in a sorted set
since: 2.0.0

ZREM key member [member ...]
summary: Remove one or more members from a sorted set
since: 1.2.0

ZREMRANGEBYLEX key min max
summary: Remove all members in a sorted set between the given lexicographical range
since: 2.8.9

ZREMRANGEBYRANK key start stop
summary: Remove all members in a sorted set within the given indexes
since: 2.0.0

ZREMRANGEBYSCORE key min max
summary: Remove all members in a sorted set within the given scores
since: 1.2.0

ZREVRANGE key start stop [WITHSCORES]
summary: Return a range of members in a sorted set, by index, with scores ordered from high to low
since: 1.2.0

ZREVRANGEBYLEX key max min [LIMIT offset count]
summary: Return a range of members in a sorted set, by lexicographical range, ordered from higher to lower strings.
since: 2.8.9

ZREVRANGEBYSCORE key max min [WITHSCORES] [LIMIT offset count]
summary: Return a range of members in a sorted set, by score, with scores ordered from high to low
since: 2.2.0

ZREVRANK key member
summary: Determine the index of a member in a sorted set, with scores ordered from high to low
since: 2.0.0

ZSCAN key cursor [MATCH pattern] [COUNT count]
summary: Incrementally iterate sorted sets elements and associated scores
since: 2.8.0

ZSCORE key member
summary: Get the score associated with the given member in a sorted set
since: 1.2.0

ZUNIONSTORE destination numkeys key [key ...] [WEIGHTS weight] [AGGREGATE SUM|MIN|MAX]
summary: Add multiple sorted sets and store the resulting sorted set in a new key
since: 2.0.0

Bloom

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BF.ADD key ...options...
summary: Help not available
since: not known

BF.EXISTS key ...options...
summary: Help not available
since: not known

BF.INSERT key ...options...
summary: Help not available
since: not known

BF.DEBUG key ...options...
summary: Help not available
since: not known

BF.MEXISTS key ...options...
summary: Help not available
since: not known

BF.INFO key ...options...
summary: Help not available
since: not known

BF.MADD key ...options...
summary: Help not available
since: not known
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redis-server --loadmodule  /opt/redis/redisbloom.so

redis

持久化

RDB

redis

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#主动触发阻塞的RDB操作（如关机，明确调用）
127.0.0.1:6379> save
#主动触发异步的RDB操作（Fork进程）
127.0.0.1:6379> bgsage

AOF

redis

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#主动触发重写AOP操作
127.0.0.1:6379> BGREWRITEAOF

常见问题

Redis如何保证Sorted_set的排序和插入效率？

底层使用跳表Skip List实现的，详细链接

Redis如何淘汰过期的keys?

Redis keys过期有两种方式：被动和主动方式。

当一些客户端尝试访问它时，key会被发现并主动的过期。

当然，这样是不够的，因为有些过期的keys，永远不会访问他们。 无论如何，这些keys应该过期，所以定时随机测试设置keys的过期时间。所有这些过期的keys将会从密钥空间删除。

具体就是Redis每秒10次做的事情：

  1. 测试随机的20个keys进行相关过期检测。
  2. 删除所有已经过期的keys。
  3. 如果有多于25%的keys过期，重复步奏1.

这是一个平凡的概率算法，基本上的假设是，我们的样本是这个密钥控件，并且我们不断重复过期检测，直到过期的keys的百分百低于25%,这意味着，在任何给定的时刻，最多会清除1/4的过期keys。

Redis如何解决缓存穿透？

布隆过滤器，采用多种映射函数将一个元素映射到bitmap的多个位中，当判断元素是否存在时，需要这些位的都是1，若有一个不为1，则不存在。

概率解决问题

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1.穿透了，不存在
2.client，增加redis中的key，value标记
3.数据库增加了元素
4.完成元素对bloom的添加

Redis的hash和JDK的hash的区别

参考资料：

redis的渐进式rehash：其重新计算hash和数据搬运的过程是发生在增删改查的操作中的，而不是集中一次性完成的。

字典rehash底层实现与Java区别

总结：

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1.Redis的Hash结构是 【数组 + 链表】，Redis的扩容和收缩，是利用两个哈希表来完成。
2.Redis字典创建时就有两个哈希表，不扩容的情况下，只使用ht[0]这个哈希表，当发生扩容和收缩时，才会用到ht[1]哈希表
3.Redis使用MurmurHash2算法来计算键的哈希值，扩容时会伴随重新计算Hash值的行为。
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//Redis字典结构
typedef struct dict{
    dictht ht[2];//哈希表，分为h[0],h[1]哈希表，通常情况下使用h[0]，h[1]用于rehash
    itn trehashidx;//rehash索引，扩容时使用，当rehash完成时，值为-1
}
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1.JDK1.8的Hash结构是 【数组 + 链表 + 红黑树】，HashMap只支持扩容，不支持收缩。
2.HashMap扩容阶段不会产生重新计算Hash值的行为。
功能 Java Redis
扩容 集中式扩容 渐进式扩容
收缩 不支持收缩 支持收缩
Hash冲突 采用链表和红黑树解决冲突 采用链表解决冲突
Hash值变化 不变 变化

Java为什么不支持收缩？
Java是以空间换时间，支持收缩不符合它的理念。

最后更新： 2021年02月26日 21:49

原始链接： https://midkuro.gitee.io/2020/05/27/redis-command/

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