Redis
String（字符串）
string是redis最基本的类型，你可以理解成与Memcached一模一样的类型，一个key对应一个value。
string类型是二进制安全的。意思是redis的string可以包含任何数据。比如jpg图片或者序列化的对象 。
string类型是Redis最基本的数据类型，一个键最大能存储512MB。
应用场景：
String是最常用的一种数据类型，普通的key/ value 存储都可以归为此类.即可以完全实现目前 Memcached 的功能，并且效率更高。还可以享受Redis的定时持久化，操作日志及 Replication等功能。除了提供与 Memcached 一样的get、set、incr、decr 等操作外，Redis还提供了下面一些操作：
- 获取字符串长度
- 往字符串append内容
- 设置和获取字符串的某一段内容
- 设置及获取字符串的某一位（bit）
- 批量设置一系列字符串的内容
command
APPEND key value
- summary: Append a value to a key
- since: 2.0.0
BITCOUNT key [start] [end]
- summary: Count set bits in a string
- since: 2.6.0
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
- 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
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
- 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 [EX seconds] [PX milliseconds] [NX|XX]
- 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
- 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