typedef struct redisObject
{
unsigned type:4;
unsigned storage:2;
/* REDIS_VM_MEMORY or REDIS_VM_SWAPPING */
unsigned encoding:4;
unsigned lru:22; /* lru time (relative to server.lruclock) */
int refcount;
void *ptr;
/* VM fields are only allocated if VM is active, otherwise the
* object allocation function will just allocate
* sizeof(redisObjct) minus sizeof(redisObjectVM), so using
* Redis without VM active will not have any overhead. */
} robj;
type 占 4 bit,用来表示 key-value 中 value 值的类型,目前 redis 支持:
string, list, set,zset,hash 5 种类型的值.
/* Object types */
#define REDIS_STRING 0
#define REDIS_LIST 1
#define REDIS_SET 2
#define REDIS_ZSET 3
#define REDIS_HASH 4
#define REDIS_VMPOINTER 8
storage 占 2 bit ,表示 此值是在 内存中,还是 swap 在硬盘上.
encoding 占 4 bit ,表示值的编码类型,目前有 8 种类型:
/* Objects encoding. Some kind of objects like Strings and Hashes can be
* internally represented in multiple ways. The 'encoding' field of the object
* is set to one of this fields for this object. */
#define REDIS_ENCODING_RAW 0 /* Raw representation */
#define REDIS_ENCODING_INT 1 /* Encoded as integer */
#define REDIS_ENCODING_HT 2 /* Encoded as hash table */
#define REDIS_ENCODING_ZIPMAP 3 /* Encoded as zipmap */
#define REDIS_ENCODING_LINKEDLIST 4 /* Encoded as regular linked
list */
#define REDIS_ENCODING_ZIPLIST 5 /* Encoded as ziplist */
#define REDIS_ENCODING_INTSET 6 /* Encoded as intset */
#define REDIS_ENCODING_SKIPLIST 7 /* Encoded as skiplist */
如 type 是 REDIS_STRING 类型的,则其值如果是数字,就可以编码
成 REDIS_ENCODING_INT,以节约内存.
如 type 是 REDIS_HASH 类 型 的 , 如 果 其 entry 小 于 配 置 值 :
hash-max-zipmap-entries 或 value 字 符 串 的 长 度 小 于
