今天复习Redis，把五种数据结构及各种数据结构的用途梳理了一遍，在这里记录一下，看看有没有你不知道的吧
一、字符串 - string
是 Redis 五种数据类型中最基本的数据类型，一个 key 对应一个 value；
常用命令
127.0.0.1:6379> set wangxiaoer wangxiaoer // 存入字符串键值对
OK
127.0.0.1:6379> mset wang wang xiao xiao er er // 批量存入字符串键值对
OK
127.0.0.1:6379> keys * // 获取所有键
1) "er"
2) "xiao"
3) "wang"
4) "wangxiaoer"
127.0.0.1:6379> setnx wang wang // 存入一个不存在的键值对（存在的话则不保存）
(integer) 0
127.0.0.1:6379> keys *
1) "er"
2) "xiao"
3) "wang"
4) "wangxiaoer"
127.0.0.1:6379> SETNX wangwang wangwang // 存入一个不存在的键值对（不存在的话则保存）
(integer) 1
127.0.0.1:6379> keys *
1) "er"
2) "xiao"
3) "wangwang"
4) "wang"
5) "wangxiaoer"
127.0.0.1:6379> get wangxiaoer // 获取一个字符串键值
"wangxiaoer"
127.0.0.1:6379> mget wang xiao er // 批量获取字符串键值
1) "wang"
2) "xiao"
3) "er"
127.0.0.1:6379> EXPIRE wangwang 5 // 设置某个键值过期时间（过期时间单位 /秒）
(integer) 1
127.0.0.1:6379> keys * // 此时还未过期
1) "er"
2) "xiao"
3) "wangwang"
4) "wang"
5) "wangxiaoer"
127.0.0.1:6379> keys * // 此时 key 为 wangwang 的键值对已过期
1) "er"
2) "xiao"
3) "wang"
4) "wangxiaoer"
127.0.0.1:6379> set wangwangwang 1
OK
127.0.0.1:6379> keys *
1) "er"
2) "xiao"
3) "wang"
4) "wangwangwang"
5) "wangxiaoer"
127.0.0.1:6379> INCR wangwangwang // 为键存储的对应的值 +1
(integer) 2
127.0.0.1:6379> INCR wangwangwang
(integer) 3
127.0.0.1:6379> get wangwangwang
"3"
127.0.0.1:6379> INCRBY wangwangwang 5 // 为键存储的对应的数字 +5
(integer) 8
127.0.0.1:6379> get wangwangwang
"8"
127.0.0.1:6379> INCR wangxiaoer // 键存储的值不是数字不能进行添加
(error) ERR value is not an integer or out of range
127.0.0.1:6379> DECR wangwangwang // 为键存储的对应的值 -1
(integer) 7
127.0.0.1:6379> get wangwangwang
"7"
127.0.0.1:6379> DECRBY wangwangwang 5 // 为键存储的对应的值 -5
(integer) 2
127.0.0.1:6379> get wangwangwang
"2"
127.0.0.1:6379> help @string // 通过help + @数据类型 获取该数据类型的命令
APPEND key value // 对某个key 存储的值进行追加（对存储的数字类型、字符串类型的值都可以进行追加）
summary: Append a value to a key
since: 2.0.0
BITCOUNT key [start end] // 获取key中存储的值转化为二进制码中偏移位范围内为二进制码为1 的个数
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
DECR key // key 存储的数字减1
summary: Decrement the integer value of a key by one
since: 1.0.0
DECRBY key decrement // key 存储的数字减 decrement（是数字）
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
GETBIT key offset
summary: Returns the bit value at offset in the string value stored at key
since: 2.2.0
GETRANGE key start end // 获取 key 存储的值长度从 start 开始 end 结束的字符串
summary: Get a substring of the string stored at a key
since: 2.4.0
GETSET key value // 获取存在的键值并设置新的值
summary: Set the string value of a key and return its old value
since: 1.0.0
INCR key // key 存储的数字加1
summary: Increment the integer value of a key by one
since: 1.0.0
INCRBY key increment // key 存储的数字加 increment（为数字）
summary: Increment the integer value of a key by the given amount
since: 1.0.0
INCRBYFLOAT key increment // key 存储的数字加 increment（为浮点数）
summary: Increment the float value of a key by the given amount
since: 2.6.0
MGET key [key ...] // 批量获取多个键的值
summary: Get the values of all the given keys
since: 1.0.0
MSET key value [key value ...] // 批量设置多个键值对
summary: Set multiple keys to multiple values
since: 1.0.1
MSETNX key value [key value ...] // 批量设置多个不存在的键值对（具有原子性）
summary: Set multiple keys to multiple values, only if none of the keys exist
since: 1.0.1
PSETEX key milliseconds value // 设置有过期时间的键值对
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] // 设置有过期时间的键值对
summary: Set the string value of a key
since: 1.0.0
SETBIT key offset value
summary: Sets or clears the bit at offset in the string value stored at key
since: 2.2.0
SETEX key seconds value // 添加不存在的键值对并设置过期时间
summary: Set the value and expiration of a key
since: 2.0.0
SETNX key value // 添加不存在的键值对
summary: Set the value of a key, only if the key does not exist
since: 1.0.0
SETRANGE key offset value // 替换指定范围内的字符串为指定的值
summary: Overwrite part of a string at key starting at the specified offset
since: 2.2.0
STRLEN key // 获取指定键的值的长度
summary: Get the length of the value stored in a key
since: 2.2.0
常用场景： 单值缓存：可以保存字符串、数字、图片信息、网址等等信息； 对象缓存：保存一个对象的json格式数据，或者保存一个对象各个属性的值
set user:1 value(json格式的数据)
mset user:1:name wangxiaoer user:1:age 18
mget user:1:name user:1:age
简单的分布式锁：
setnx user:1 true // 设置成功返回1，设置失败返回0,
执行业务代码 // 上面的设置成功后执行
del user:1 // 执行成功后删除锁（key）
为了防止死锁，在设置时还可以设置键值对的过期时间，过期释放
计数器：微信公众号文章被阅读、点赞、在看的次数
incrby article:xxxx:read // 阅读
incrby article:xxxx:praise // 点赞
incrby article:xxxx:share // 在看
分布式系统全局序列号：获取后放在本地内存进行使用，使用完毕后再进行获取
incrby serialUID 1000 // 一次性多取一些值，节省redis的性能
二、哈希 - hash
键值是一个map，值本身也是一个map，具体结构如下：
常用命令 命令都是以h开头：
127.0.0.1:6379> hset user name wangxiaoer // 存储一个hash表key的键值
(integer) 1
127.0.0.1:6379> hsetnx user name wangxiaoer // 存储一个不存在的hash表key的键值
(integer) 0
127.0.0.1:6379> hset user age 18
(integer) 1
127.0.0.1:6379> hset user gender 男
(integer) 1
127.0.0.1:6379> hget user name // 获取hash表中key对应的filed的值
"wangxiaoer"
127.0.0.1:6379> HSETNX user1 name xiaoer
(integer) 1
127.0.0.1:6379> HMSET user1 age 18 gender 男
OK
127.0.0.1:6379> hlen user
(integer) 3
127.0.0.1:6379> HGETALL user // 获取hash表key中所有的值
1) "name"
2) "wangxiaoer"
3) "age"
4) "18"
5) "gender"
6) "\xe7\x94\xb7"
127.0.0.1:6379> HINCRBY user age 12
(integer) 30
127.0.0.1:6379> hmset user 1:name wang 1:age 18 2:name xiao 2:age 19 // 批量设置
OK
127.0.0.1:6379> HGETALL user
1) "1:name"
2) "wang"
3) "1:age"
4) "18"
5) "2:name"
6) "xiao"
7) "2:age"
8) "19"
127.0.0.1:6379> Help @hash // 通过help + @数据类型 获取该数据类型的命令
HDEL key field [field ...] // 批量删除hash表中key中filed对应的键值
summary: Delete one or more hash fields
since: 2.0.0
HEXISTS key field // 判断hash表中的filed是否存在对应的键值
summary: Determine if a hash field exists
since: 2.0.0
HGET key field // 获取hash表中的filed对应的键值
summary: Get the value of a hash field
since: 2.0.0
HGETALL key // 获取hash表key中所有的值
summary: Get all the fields and values in a hash
since: 2.0.0
HINCRBY key field increment // 对hash表中的filed对应的数字键值添加 increment
summary: Increment the integer value of a hash field by the given number
since: 2.0.0
HINCRBYFLOAT key field increment // 对hash表中的filed对应的数字键值添加 increment（浮点数）
summary: Increment the float value of a hash field by the given amount
since: 2.6.0
HKEYS key // 获取hash表中所有的filed
summary: Get all the fields in a hash
since: 2.0.0
HLEN key // 获取hash表中filed 的数量
summary: Get the number of fields in a hash
since: 2.0.0
HMGET key field [field ...] // 批量获取hash表中的filed对应的键值
summary: Get the values of all the given hash fields
since: 2.0.0
HMSET key field value [field value ...] // 批量设置hash表中的filed对应的键值
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 // 设置hash表中的filed对应的键值
summary: Set the string value of a hash field
since: 2.0.0
HSETNX key field value // 设置hash表中不存在的filed对应的键值
summary: Set the value of a hash field, only if the field does not exist
since: 2.0.0
HSTRLEN key field // 获取hash表中filed 的键值的长度
summary: Get the length of the value of a hash field
since: 3.2.0
HVALS key // 获取hash表key中所有的值（不包括filed）
summary: Get all the values in a hash
since: 2.0.0
常用场景
对象存储：
hmset user 1:name wangxiaoer 1:age 18
电商购物车：
以用户id为key 以商品信息为field 以商品的数量为value
购物车操作如下：
添加商品：hset cart:1001 10086 1
增加商品数量：hincrby cart:1001 10086 1
获取商品总数：hlen cart:1001
删除商品：hdel cart:1001 10086
获取购物车中的所有商品：hgetall cart:10086
hash 与 string 的比较 优点：
同类数据归类整合存储，方便数据管理；
相比 string 操作消耗内存与 CPU 更小；
相比 string 存储更节省空间；
缺点：
过期功能只能作用在key上，不能使用在field上；
Redis 集群架构下不适合大规模使用（会出现数据倾斜）；
三、列表 - list
其实就是链表，而且是双端链表，表中的元素是有序的，切元素是可以重复的，表的左右两端都可以进行插入和删除操作； 常用命令 命令通常是以l开头：
127.0.0.1:6379> LPUSH wang 12 23 34 45 56 56 57 // 将一个或者多个value插入到key列表的表头（左侧）
(integer) 7
127.0.0.1:6379> RPUSH wang 75 75 65 54 43 32 21 // 将一个或者多个value插入到key列表的表尾（右侧）
(integer) 14
127.0.0.1:6379> LPOP wang // 从表头取出一个元素
"57"
127.0.0.1:6379> RPOP wang // 从表头尾出一个元素
"21"
127.0.0.1:6379> BLPOP wang 5 // 从表头取出一个元素，若列表中无元素则阻塞指定时间
1) "wang"
2) "56"
127.0.0.1:6379> BRPOP wang 5 // 从表尾取出一个元素，若列表中无元素则阻塞指定时间
1) "wang"
2) "32"
127.0.0.1:6379> LRANGE wang 0 -1 // 取出指定范围内的元素（表头为下标为0，表尾为-1）
1) "56"
2) "45"
3) "34"
4) "23"
5) "12"
6) "75"
7) "75"
8) "65"
9) "54"
10) "43"
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 // 从一个链表的表尾取出一个元素插入另一个链表的表头，如果取不到则阻塞指定时间
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 // 获取链表指定下标的元素
summary: Get an element from a list by its index
since: 1.0.0
LINSERT key BEFORE|AFTER pivot value // 在指定元素的前方或者后方插入一个value
summary: Insert an element before or after another element in a list
since: 2.2.0
LLEN key // 获取列表的长度
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 // 向已存在的列表中添加元素value
summary: Prepend a value to a list, only if the list exists
since: 2.2.0
LRANGE key start stop // 获取链表指定范围内的元素（超出范围则取出范围内存在的全部元素）
summary: Get a range of elements from a list
since: 1.0.0
LREM key count value // 移除链表中指定数量的指定值
summary: Remove elements from a list
since: 1.0.0
LSET key index value // 将链表中指定下标的值设置为指定值（超出范围则报错）
summary: Set the value of an element in a list by its index
since: 1.0.0
LTRIM key start stop // 移除链表中指定范围内的所有元素
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 // 从一个链表的表尾取出一个元素插入另一个链表的表头
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
常用场景 常用的数据结构：
Stack（栈）：LPUSH + LPOP
Queue（队列）：LPUSH + RPOP
Blocking Queue（阻塞队列）：LPUSH + BRPOP
微博或者订阅号的消息流（栈）：
先收到的消息放在后面，后收到（最新）的消息排在最前面
四、集合 - set
和 list 一样的是也存储多个元素，不同的是：元素不能重复，元素是无序的，支持集合间操作（交集、并集、差集） 常用命令
127.0.0.1:6379> SADD wang 12 12 12 12 23 34 45 56 // 向集合中添加一个或者多个元素（重复的元素会去除）
(integer) 5
127.0.0.1:6379> SREM wang 12 // 从集合中移除某个元素
(integer) 1
127.0.0.1:6379> SMEMBERS wang // 获取指定集合中的所有元素
1) "23"
2) "34"
3) "45"
4) "56"
127.0.0.1:6379> SCARD wang // 获取集合中元素的数量
(integer) 4
127.0.0.1:6379> SISMEMBER wang 12 // 判断元素是否在集合中
(integer) 0
127.0.0.1:6379> SISMEMBER wang 23
(integer) 1
127.0.0.1:6379> SRANDMEMBER wang 2 // 获取集合中指定数量的元素（无序）
1) "34"
2) "23"
127.0.0.1:6379> SRANDMEMBER wang 2
1) "45"
2) "23"
127.0.0.1:6379> SPOP wang 2 // 取出集合中指定数量的元素（无序）
1) "45"
2) "34"
127.0.0.1:6379> SADD xiaoer 12 23 34 56 67 78
(integer) 6
127.0.0.1:6379> SINTER wang xiaoer // 对两个集合取交集
1) "23"
2) "56"
127.0.0.1:6379> SINTERSTORE wangxiaoer wang xiaoer // 对两个集合取交集并存储为新的集合
(integer) 2
127.0.0.1:6379> SRANDMEMBER wangxiaoer 3
1) "23"
2) "56"
127.0.0.1:6379> SUNION wang xiaoer // 对两个集合取并集
1) "12"
2) "23"
3) "34"
4) "56"
5) "67"
6) "78"
127.0.0.1:6379> SDIFF wang xiaoer // 对两个集合取差集
(empty list or set)
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 ...] // 将两个集合的差集存储为新的集合
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 // 将集合中的元素移动到另一个集合中
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] // 对集合中的元素匹配指定数量指定格式的元素
summary: Incrementally iterate Set elements
since: 2.8.0
SUNION key [key ...]
summary: Add multiple sets
since: 1.0.0
SUNIONSTORE destination key [key ...] // 取两个集合的交集并存储为新的集合
summary: Add multiple sets and store the resulting set in a key
since: 1.0.0
常用场景
抽奖小程序：
将参与的人员添加到抽奖池中：SADD lottery wangxiaoer
查看奖池中人员信息：SMEMBERS lottery
从奖池中抽2人（人员不移除）：SRANDMEMBER lottery 2
从奖池中抽2人（人员移除）：SPOP lottery 2
微信点赞标签：
点赞：SADD like:article001 userId
取消点赞：SREM like:article001 userId
检查用户是否点过赞：SISMEMBER like:article001 userId
获取点赞的用户列表：SMEMBERS like:article001
获取点赞用户数：SCARD like:article001
微博关注模型：
获取 wangxiaoer 关注的人：SMEMBERS wangxiaoer
获取 gaoyuanyuan 关注的人：SMEMBERS gaoyuanyuan
获取 zhangziyi 关注的人：SMEMBERS zhangziyi
获取 wangxiaoer 和 gaoyuanyuan 共同关注的人：SINTER wangxiaoer gaoyuanyuan
获取 wangxiaoer 关注的也关注 gaoyuanyuan 的人：SISMEMNER zhangziyi gaoyuanyuan
获取 wangxiaoer 可能认识的人：SDIFF gaoyuanyuan wangxiaoer
商品筛选：
添加品牌：SADD brand:huawei mate40
添加新旧：SADD oldnew:new mate40
添加尺寸：SADD size:6.1 mate40
获取华为新的6.1存的手机：SINTER brand:huawei oldnew:new size:6.1
五、有序集合 - zset
有序集合是一种特殊的集合，保留了集合中元素不能重复的属性，区别是集合中的元素是可以排序的； 常用命令 命令通常以z开头：
127.0.0.1:6379> ZADD wang 1 wang 2 xiao 3 er // 向集合中添加指定分值的值
(integer) 3
127.0.0.1:6379> ZREM wang wang // 移除集合中指定的元素
(integer) 1
127.0.0.1:6379> ZSCORE wang xiao // 获取集合中指定的元素的分值
"2"
127.0.0.1:6379> ZINCRBY wang 3 xiao // 对集合中指定元素添加指定的数值
"5"
127.0.0.1:6379> ZCARD wang // 获取集合中元素的数量
(integer) 2
127.0.0.1:6379> ZRANGE wang 1 2 // 获取集合中指定范围内的元素（正序）
1) "xiao"
127.0.0.1:6379> ZREVRANGE wang 0 2 // 获取集合中指定范围内的元素（倒序）
1) "xiao"
2) "er"
127.0.0.1:6379> ZADD xiao 3 xiao 5 er
(integer) 2
127.0.0.1:6379> ZINTERSTORE wangxiao 2 wang xiao // 获取两个集合中元素的交集并存储
(integer) 2
127.0.0.1:6379> ZRANGE wangxiao 0 -1
1) "er"
2) "xiao"
127.0.0.1:6379> help @sorted_set
BZPOPMAX key [key ...] timeout // 从一个或者多个集合中移除分数最高的元素，如果没有则阻塞（指定时间）
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 // 从一个或者多个集合中移除分数最低的元素，如果没有则阻塞（指定时间）
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 // 统计集合中指定分数范围内的元素数量
summary: Count the members in a sorted set with scores within the given values
since: 2.0.0
ZINCRBY key increment member // 对集合中指定元素增加指定的数值
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 // 统计集合中指定词典范围内的元素数量
summary: Count the number of members in a sorted set between a given lexicographical range
since: 2.8.9
ZPOPMAX key [count] // 移除指定集合中移除指定数量最高分数的值
summary: Remove and return members with the highest scores in a sorted set
since: 5.0.0
ZPOPMIN key [count] // 移除指定集合中移除指定数量最低分数的值
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
常用场景
排行榜：
点击新闻：ZADD hostnews:20201108 1 telangpu
获取某天排行前十的新闻：ZREVRANGE hostnews:20201108 0 9 WITHSCORES
备注： redis的key的类型为SDS（Simple Dynamic String：简单的动态字符串），该key值的长度会动态扩充，容量不够时长度会翻倍（达到1Mb时，每次扩容增加1Mb）;
