讲讲Redis各个数据类型的底层数据结构

typedef char *sds;

/* Note: sdshdr5 is never used, we just access the flags byte directly.
 * However is here to document the layout of type 5 SDS strings. */
struct __attribute__ ((__packed__)) sdshdr5 {
    unsigned char flags; /* 3 lsb of type, and 5 msb of string length */
    char buf[];
};
struct __attribute__ ((__packed__)) sdshdr8 {
    uint8_t len; /* used */
    uint8_t alloc; /* excluding the header and null terminator */
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    char buf[];
};
struct __attribute__ ((__packed__)) sdshdr16 {
    uint16_t len; /* used */
    uint16_t alloc; /* excluding the header and null terminator */
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    char buf[];
};
struct __attribute__ ((__packed__)) sdshdr32 {
    uint32_t len; /* used */
    uint32_t alloc; /* excluding the header and null terminator */
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    char buf[];
};
struct __attribute__ ((__packed__)) sdshdr64 {
    uint64_t len; /* used */
    uint64_t alloc; /* excluding the header and null terminator */
    unsigned char flags; /* 3 lsb of type, 5 unused bits */
    char buf[];
};

/* 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 list {
    listNode *head;  //链表头节点指针
    listNode *tail;  //链表尾节点指针
    void *(*dup)(void *ptr); // 用于复制链表节点所保存的值
    void (*free)(void *ptr); // 用于释放链表节点所保存的值
    int (*match)(void *ptr, void *key); //用于对比链表节点所保存的值和另一个输入值是否相等
    unsigned long len; // 链表所包含的节点数量
} list;

//字典结构
typedef struct dict {
    dictType *type; // 类型特定的函数
    void *privdata;  //私有数据
    dictht ht[2]; //长度为2的哈希表数组， 一般情况下字典仅使用 ht[0]哈希表， ht[1]在rehash的时候会使用到。
    long rehashidx; /* 未进行rehash的时候 rehashidx == -1 */
    unsigned long iterators; /* number of iterators currently running */
} dict;

//哈希表结构
typedef struct dictht {
    dictEntry **table; //哈希数组
    unsigned long size; //哈希表大小
    unsigned long sizemask; //哈希表掩码，用于计算索引值， 总是等于size-1
    unsigned long used; //表示已有节点数量
} dictht;

//哈希节点
typedef struct dictEntry {
    void *key; //键
    union { //value值，包含了多种类型的值，不同类型的值可以使用不同的数据结构存储，节省内存。
        void *val;  //其值可以是一个指针
        uint64_t u64; //其值也可以是一个uint64_t 整数
        int64_t s64; //其值可以是一个int64_t 整数
        double d; //其值可以是一个double 
    } v;
    struct dictEntry *next; //指向像一个哈希节点
} dictEntry;

typedef struct zskiplistNode { //跳跃表节点
    sds ele; //成员对象，各个节点中成员对象唯一的。
    double score; //分值
    struct zskiplistNode *backward; //后退指针
    struct zskiplistLevel { //层， 最大32层
        struct zskiplistNode *forward; //前进指针
        unsigned long span; //跨度
    } level[];
} zskiplistNode;

typedef struct zskiplist { //跳跃表
    struct zskiplistNode *header, *tail;//指向 跳跃表头 和表尾节点
    unsigned long length; // 节点数量
    int level; //跳跃表中层数最大的节点层数量
} zskiplist;

typedef struct zset { // zset的数据结构使用了 字典dict 和 zskiplist
    dict *dict;
    zskiplist *zsl;
} zset;

typedef struct quicklist {
    quicklistNode *head;
    quicklistNode *tail;
    unsigned long count;        /* total count of all entries in all ziplists */
    unsigned long len;          /* number of quicklistNodes */
    int fill : QL_FILL_BITS;              /* fill factor for individual nodes */
    unsigned int compress : QL_COMP_BITS; /* depth of end nodes not to compress;0=off */
    unsigned int bookmark_count: QL_BM_BITS;
    quicklistBookmark bookmarks[];
} quicklist;

typedef struct quicklistBookmark {
    quicklistNode *node;
    char *name;
} quicklistBookmark;

typedef struct quicklistNode {
    struct quicklistNode *prev;
    struct quicklistNode *next;
    unsigned char *zl;
    unsigned int sz;             /* ziplist size in bytes */
    unsigned int count : 16;     /* count of items in ziplist */
    unsigned int encoding : 2;   /* RAW==1 or LZF==2 */
    unsigned int container : 2;  /* NONE==1 or ZIPLIST==2 */
    unsigned int recompress : 1; /* was this node previous compressed? */
    unsigned int attempted_compress : 1; /* node can't compress; too small */
    unsigned int extra : 10; /* more bits to steal for future usage */
} quicklistNode;

typedef struct intset {
    uint32_t encoding;
    uint32_t length;
    int8_t contents[];
} intset;