本文基于Redis 3.0源码和《Redis设计与实现》一书进行分析，涵盖了Redis中五种主要对象类型（String、List、Set、Hash、Sorted Set）及其底层数据结构的详细解析。

对象系统

Redis的对象系统由redisObject结构表示，该结构包含三个与保存数据相关的属性：type、encoding和ptr。每种对象类型都对应至少一种底层数据结构，以确保高效存储和访问。

/* Object types */
#define REDIS_STRING 0
#define REDIS_LIST 1
#define REDIS_SET 2
#define REDIS_ZSET 3
#define REDIS_HASH 4
/* Objects encoding. Some kinds of objects like Strings and Hashes can be internally represented in multiple ways. The 'encoding' field of the object is set to one of these 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 */
#define REDIS_ENCODING_EMBSTR 8 /* Embedded sds string encoding */
typedef struct redisObject {
unsigned type:4;
unsigned encoding:4;
unsigned lru:REDIS_LRU_BITS; /* lru time (relative to server.lruclock) */
int refcount;
void *ptr;
} robj;


底层数据结构

SDS - Simple Dynamic String

SDS是二进制安全的动态字符串，具有高效的内存管理和字符串操作功能。

定义

typedef char *sds;
struct sdshdr {
unsigned int len;
unsigned int free;
char buf[];
};


API

/* Append the specified binary-safe string pointed by 't' of 'len' bytes to the end of the specified sds string 's'.
* After the call, the passed sds string is no longer valid and all the references must be substituted with the new pointer returned by the call. */
sds sdscatlen(sds s, const void *t, size_t len) {
struct sdshdr *sh;
size_t curlen = sdslen(s);
s = sdsMakeRoomFor(s,len);
if (s == NULL) return NULL;
sh = (void*) (s-(sizeof(struct sdshdr)));
memcpy(s+curlen, t, len);
sh->len = curlen+len;
sh->free = sh->free-len;
s[curlen+len] = '\0';
return s;
}
/* Append the specified null terminated C string to the sds string 's'.
* After the call, the passed sds string is no longer valid and all the references must be substituted with the new pointer returned by the call. */
sds sdscat(sds s, const char *t) {
return sdscatlen(s, t, strlen(t));
}

链表（Linked List）

链表是一种常见的线性数据结构，Redis中的链表实现支持双向遍历和节点插入删除操作。

/* Node, List, and Iterator are the only data structures used currently. */
typedef struct listNode {
struct listNode *prev;
struct listNode *next;
void *value;
} listNode;
typedef struct listIter {
listNode *next;
int direction;
} listIter;
typedef struct list {
listNode *head;
listNode *tail;
void *(*dup)(void *ptr);
void (*free)(void *ptr);
int (*match)(void *ptr, void *key);
unsigned long len;
} list;