面试遇到 Redis，我作为小白是这么被“刁难”的！｜还可以学到什么（1）？

typedef struct redisObject {
    // 类型
    unsigned type:4;
    // 编码
    unsigned encoding:4;
    // 指向数据的指针
    void *ptr;

    // 记录对象最后一次被程序访问时间，用于计算空转时长(当前时间-lru)
    unsigned lru:22; /* lru time (relative to server.lruclock) */
    // 引用计数，用于内存回收
    int refcount;
} robj;

# 键为字符串对象，值为字符串对象

redis> SET msg "hello world"
OK

redis> TYPE msg
string

# 键为字符串对象，值为列表对象

redis> RPUSH numbers 1 3 5
(integer) 6

redis> TYPE numbers
list

# 键为字符串对象，值为哈希对象

redis> HMSET profile name Tome age 25 career Programmer
OK

redis> TYPE profile
hash

# 键为字符串对象，值为集合对象

redis> SADD fruits apple banana cherry
(integer) 3

redis> TYPE fruits
set

# 键为字符串对象，值为有序集合对象

redis> ZADD price 8.5 apple 5.0 banana 6.0 cherry
(integer) 3

redis> TYPE price
zset
/* Object types */
// 对象类型
#define REDIS_STRING 0
#define REDIS_LIST 1
#define REDIS_SET 2
#define REDIS_ZSET 3
#define REDIS_HASH 4

 rewriteAppendOnlyFile(char *filename) {
   
 if (o->type == REDIS_STRING) {
                /* Emit a SET command */
                char cmd[]="*3\r\n$3\r\nSET\r\n";
                if (rioWrite(&aof,cmd,sizeof(cmd)-1) == 0) goto werr;
                /* Key and value */
                if (rioWriteBulkObject(&aof,&key) == 0) goto werr;
                if (rioWriteBulkObject(&aof,o) == 0) goto werr;
            } else if (o->type == REDIS_LIST) {
                if (rewriteListObject(&aof,&key,o) == 0) goto werr;
            } else if (o->type == REDIS_SET) {
                if (rewriteSetObject(&aof,&key,o) == 0) goto werr;
            } else if (o->type == REDIS_ZSET) {
                if (rewriteSortedSetObject(&aof,&key,o) == 0) goto werr;
            } else if (o->type == REDIS_HASH) {
                if (rewriteHashObject(&aof,&key,o) == 0) goto werr;
            } else {
                redisPanic("Unknown object type");
            }

/* 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. */
// 对象编码
#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 */

/* Save a Redis object. Returns -1 on error, 0 on success. 
 *
 * 将给定对象 o 保存到 rdb 中。
 *
 * 保存成功返回 rdb 保存该对象所需的字节数 ，失败返回 0 。
 *
 * p.s.上面原文注释所说的返回值是不正确的
 */
int rdbSaveObject(rio *rdb, robj *o) {
    int n, nwritten = 0;

    // 保存字符串对象
    if (o->type == REDIS_STRING) {
        /* Save a string value */
        if ((n = rdbSaveStringObject(rdb,o)) == -1) return -1;
        nwritten += n;

    // 保存列表对象
    } else if (o->type == REDIS_LIST) {
        /* Save a list value */
        if (o->encoding == REDIS_ENCODING_ZIPLIST) {
            size_t l = ziplistBlobLen((unsigned char*)o->ptr);

            // 以字符串对象的形式保存整个 ZIPLIST 列表
            if ((n = rdbSaveRawString(rdb,o->ptr,l)) == -1) return -1;
            nwritten += n;
        } else if (o->encoding == REDIS_ENCODING_LINKEDLIST) {
            list *list = o->ptr;
            listIter li;
            listNode *ln;

            if ((n = rdbSaveLen(rdb,listLength(list))) == -1) return -1;
            nwritten += n;

            // 遍历所有列表项
            listRewind(list,&li);
            while((ln = listNext(&li))) {
                robj *eleobj = listNodeValue(ln);
                // 以字符串对象的形式保存列表项
                if ((n = rdbSaveStringObject(rdb,eleobj)) == -1) return -1;
                nwritten += n;
            }
        } else {
            redisPanic("Unknown list encoding");
        }

    // 保存集合对象
    } else if (o->type == REDIS_SET) {
        /* Save a set value */
        if (o->encoding == REDIS_ENCODING_HT) {
            dict *set = o->ptr;
            dictIterator *di = dictGetIterator(set);
            dictEntry *de;

            if ((n = rdbSaveLen(rdb,dictSize(set))) == -1) return -1;
            nwritten += n;

            // 遍历集合成员
            while((de = dictNext(di)) != NULL) {
                robj *eleobj = dictGetKey(de);
                // 以字符串对象的方式保存成员
                if ((n = rdbSaveStringObject(rdb,eleobj)) == -1) return -1;
                nwritten += n;
            }
            dictReleaseIterator(di);
        } else if (o->encoding == REDIS_ENCODING_INTSET) {
            size_t l = intsetBlobLen((intset*)o->ptr);

            // 以字符串对象的方式保存整个 INTSET 集合
            if ((n = rdbSaveRawString(rdb,o->ptr,l)) == -1) return -1;
            nwritten += n;
        } else {
            redisPanic("Unknown set encoding");
        }

    // 保存有序集对象
    } else if (o->type == REDIS_ZSET) {
        /* Save a sorted set value */
        if (o->encoding == REDIS_ENCODING_ZIPLIST) {
            size_t l = ziplistBlobLen((unsigned char*)o->ptr);

            // 以字符串对象的形式保存整个 ZIPLIST 有序集
            if ((n = rdbSaveRawString(rdb,o->ptr,l)) == -1) return -1;
            nwritten += n;
        } else if (o->encoding == REDIS_ENCODING_SKIPLIST) {
            zset *zs = o->ptr;
            dictIterator *di = dictGetIterator(zs->dict);
            dictEntry *de;

            if ((n = rdbSaveLen(rdb,dictSize(zs->dict))) == -1) return -1;
            nwritten += n;

            // 遍历有序集
            while((de = dictNext(di)) != NULL) {
                robj *eleobj = dictGetKey(de);
                double *score = dictGetVal(de);

                // 以字符串对象的形式保存集合成员
                if ((n = rdbSaveStringObject(rdb,eleobj)) == -1) return -1;
                nwritten += n;

                // 成员分值（一个双精度浮点数）会被转换成字符串
                // 然后保存到 rdb 中
                if ((n = rdbSaveDoubleValue(rdb,*score)) == -1) return -1;
                nwritten += n;
            }
            dictReleaseIterator(di);
        } else {
            redisPanic("Unknown sorted set encoding");
        }

    // 保存哈希表
    } else if (o->type == REDIS_HASH) {

        /* Save a hash value */
        if (o->encoding == REDIS_ENCODING_ZIPLIST) {
            size_t l = ziplistBlobLen((unsigned char*)o->ptr);

            // 以字符串对象的形式保存整个 ZIPLIST 哈希表
            if ((n = rdbSaveRawString(rdb,o->ptr,l)) == -1) return -1;
            nwritten += n;

        } else if (o->encoding == REDIS_ENCODING_HT) {
            dictIterator *di = dictGetIterator(o->ptr);
            dictEntry *de;

            if ((n = rdbSaveLen(rdb,dictSize((dict*)o->ptr))) == -1) return -1;
            nwritten += n;

            // 迭代字典
            while((de = dictNext(di)) != NULL) {
                robj *key = dictGetKey(de);
                robj *val = dictGetVal(de);

                // 键和值都以字符串对象的形式来保存
                if ((n = rdbSaveStringObject(rdb,key)) == -1) return -1;
                nwritten += n;
                if ((n = rdbSaveStringObject(rdb,val)) == -1) return -1;
                nwritten += n;
            }
            dictReleaseIterator(di);

        } else {
            redisPanic("Unknown hash encoding");
        }

    } else {
        redisPanic("Unknown object type");
    }

    return nwritten;
}

redis> SET msg "hello wrold"
OK

redis> OBJECT ENCODING msg
"embstr"

redis> SET story "long long long long long long ago ..."
OK

redis> OBJECT ENCODING story
"raw"

//存放的是整数类型,编码类是：intset
127.0.0.1:6379> SADD numbers 1 3 5
(integer) 3
127.0.0.1:6379> OBJECT ENCODING numbers
"intset"

//存放的是字符串类型,编码类是：hashtable，代表是无序 唯一。
127.0.0.1:6379> SADD numbers "seven"
(integer) 1
127.0.0.1:6379> OBJECT ENCODING numbers
"hashtable"
//超过512整数，编码类是：hashtable
127.0.0.1:6379> EVAL "for i=1, 512 do redis.call('SADD', KEYS[1], i) end" 1 integers
(nil)
127.0.0.1:6379> OBJECT ENCODING integers
"intset"
127.0.0.1:6379> SADD integers 10086
(integer) 1
127.0.0.1:6379> OBJECT ENCODING integers
"hashtable"
127.0.0.1:6379>
http://redisbook.com/preview/object/set.html

//有序集合保存的元素数量小于 128 个
127.0.0.1:6379> ZADD price 8.5 apple 5.0 banana 6.0 cherry
(integer) 3
127.0.0.1:6379> object encoding price
"ziplist"
127.0.0.1:6379> type price
zset


# 对象包含了 128 个元素
redis> EVAL "for i=1, 128 do redis.call('ZADD', KEYS[1], i, i) end" 1 numbers
(nil)

redis> ZCARD numbers
(integer) 128

redis> OBJECT ENCODING numbers
"ziplist"

# 再添加一个新元素
redis> ZADD numbers 3.14 pi
(integer) 1

# 对象包含的元素数量变为 129 个
redis> ZCARD numbers
(integer) 129

# 编码已改变
redis> OBJECT ENCODING numbers
"skiplist"

# 向有序集合添加一个成员只有三字节长的元素
redis> ZADD blah 1.0 www
(integer) 1

redis> OBJECT ENCODING blah
"ziplist"

# 向有序集合添加一个成员为 66 字节长的元素
redis> ZADD blah 2.0 oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
(integer) 1

# 编码已改变
redis> OBJECT ENCODING blah
"skiplist"

typedef struct redisObject {
    // 类型
    unsigned type:4;
    // 编码
    unsigned encoding:4;
    // 指向数据的指针
    void *ptr;

    // 记录对象最后一次被程序访问时间，用于计算空转时长(当前时间-lru)
    unsigned lru:22; /* lru time (relative to server.lruclock) */
    // 引用计数，用于内存回收
    int refcount;
} robj;

//01 geoadd key 经度 纬度 地理位置
127.0.0.1:6379> geoadd china:city 116.40 39.90 beijing 121.47 32.23 shanghai
(integer) 2
//02 geopos命令：从key里返回所有给定位置元素的位置（经度和纬度） 
127.0.0.1:6379> geopos china:city beijing
1) 1) "116.39999896287918091"
   2) "39.90000009167092543"
  
//03 georadius命令：以给定的经纬度为中心，找出某一半径内的元素 
127.0.0.1:6379> georadius china:city 116 39  1000 km
1) "shanghai"
2) "beijing"

//04 geohash命令：返回一个或多个位置元素的Geohash字符串
127.0.0.1:6379> geohash china:city beijing
1) "wx4fbxxfke0"
Geohash字符串查询
http://geohash.org/wx4fbxxfke0


127.0.0.1:6379> debug object china:city
Value at:0x7f2ad2c285c0 refcount:1
 encoding:ziplist 
serializedlength:51 
lru:4668404 
lru_seconds_idle:5768

/* GEOADD key long lat name [long2 lat2 name2 ... longN latN nameN] */
void geoaddCommand(client *c) {
  

    int elements = (c->argc - 2) / 3;
    int argc = 2+elements*2; /* ZADD key score ele ... */
    robj **argv = zcalloc(argc*sizeof(robj*));
    argv[0] = createRawStringObject("zadd",4);
    argv[1] = c->argv[1]; /* key */
    incrRefCount(argv[1]);

    /* Create the argument vector to call ZADD in order to add all
     * the score,value pairs to the requested zset, where score is actually
     * an encoded version of lat,long. */
    int i;
    for (i = 0; i < elements; i++) {
        double xy[2];

        if (extractLongLatOrReply(c, (c->argv+2)+(i*3),xy) == C_ERR) {
            for (i = 0; i < argc; i++)
                if (argv[i]) decrRefCount(argv[i]);
            zfree(argv);
            return;
        }

        /* Turn the coordinates into the score of the element. */
        GeoHashBits hash;
        geohashEncodeWGS84(xy[0], xy[1], GEO_STEP_MAX, &hash);
        GeoHashFix52Bits bits = geohashAlign52Bits(hash);
        //score设置
        robj *score = createObject(OBJ_STRING, sdsfromlonglong(bits));
        robj *val = c->argv[2 + i * 3 + 2];
        argv[2+i*2] = score;//坐标
        argv[3+i*2] = val;//
        incrRefCount(val);
    }

    /* Finally call ZADD that will do the work for us. */
    replaceClientCommandVector(c,argc,argv);
    zaddCommand）//zset存储
}