Redis原理(二) Redis的对象类型及其内部编码

Redis 支持 5 种对象类型，而每种结构都有至少两种编码。

这样做的好处在于：一方面接口与实现分离，当需要增加或改变内部编码时，用户使用不受影响，另一方面可以根据不同的应用场景切换内部编码，提高效率。

Redis 各种对象类型支持的内部编码官网描述：

Strings can be encoded as raw (normal string encoding) or int (strings representing integers in a 64 bit signed interval are encoded in this way in order to save space).

Lists can be encoded as ziplist or linkedlist. The ziplist is the special representation that is used to save space for small lists.

Sets can be encoded as intset or hashtable. The intset is a special encoding used for small sets composed solely of integers.

Hashes can be encoded as ziplist or hashtable. The ziplist is a special encoding used for small hashes.

Sorted Sets can be encoded as ziplist or skiplist format. As for the List type small sorted sets can be specially encoded using ziplist, while the skiplist encoding is the one that works with sorted sets of any size.

翻译如下表格：

类型	编码	对象
String	int	整数值实现
String	embstr	sds实现 <=39 字节
String	raw	sds实现 > 39字节
List	ziplist	压缩列表实现
List	linkedlist	双端链表实现
Set	intset	整数集合使用
Set	hashtable	字典实现
Hash	ziplist	压缩列表实现
Hash	hashtable	字典使用
Sorted set	zipl