RedisObject详解

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Redis中任意数据类型的键和值都会被封装成一个RedisObject，也叫作Redis对象，结构如下

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// server.h
struct redisObject {	
    unsigned type:4;				// 对象类型
    unsigned encoding:4;			// 编码类型
    unsigned lru:LRU_BITS; 			// lru时间，用于内存回收
    int refcount;					// 引用计数器，用于判断是否可以回收
    void *ptr;						// 指针，指向存放实际数据的空间
};
  • 可以看出，一个Redis对象头为16字节

type:

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// server.h
#define OBJ_STRING 0    /* String object. */
#define OBJ_LIST 1      /* List object. */
#define OBJ_SET 2       /* Set object. */
#define OBJ_ZSET 3      /* Sorted set object. */
#define OBJ_HASH 4      /* Hash object. */

Encoding：

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// server.h
#define OBJ_ENCODING_RAW 0     /* Raw representation */
#define OBJ_ENCODING_INT 1     /* Encoded as integer */
#define OBJ_ENCODING_HT 2      /* Encoded as hash table */
#define OBJ_ENCODING_ZIPMAP 3  /* No longer used: old hash encoding. */
#define OBJ_ENCODING_LINKEDLIST 4 /* No longer used: old list encoding. */
#define OBJ_ENCODING_ZIPLIST 5 /* No longer used: old list/hash/zset encoding. */
#define OBJ_ENCODING_INTSET 6  /* Encoded as intset */
#define OBJ_ENCODING_SKIPLIST 7  /* Encoded as skiplist */
#define OBJ_ENCODING_EMBSTR 8  /* Embedded sds string encoding */
#define OBJ_ENCODING_QUICKLIST 9 /* Encoded as linked list of listpacks */
#define OBJ_ENCODING_STREAM 10 /* Encoded as a radix tree of listpacks */
#define OBJ_ENCODING_LISTPACK 11 /* Encoded as a listpack */
#define OBJ_ENCODING_LISTPACK_EX 12 /* Encoded as listpack, extended with metadata */