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typedef struct redisObject {
  unsigned type : 4;
  unsigned encoding : 4;
  int refcount;
  void *ptr;
} robj;


类型常量	对象的名称
REDIS_STRING 字符串对象
REDIS_LIST	列表对象
REDIS_HASH	哈希对象
REDIS_SET	集合对象
REDIS_ZSET	有序集合对象
    

/* 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 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     /* Encoded as zipmap */
#define OBJ_ENCODING_LINKEDLIST 4 /* No longer used: old list encoding. */
#define OBJ_ENCODING_ZIPLIST 5    /* Encoded as ziplist */
#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 ziplists */
#define OBJ_ENCODING_STREAM 10    /* Encoded as a radix tree of listpacks */


char *rdb_type_string[] = {
    "string",
    "list-linked",
    "set-hashtable",
    "zset-v1",
    "hash-hashtable",
    "zset-v2",
    "module-value",
    "","",
    "hash-zipmap",
    "list-ziplist",
    "set-intset",
    "zset-ziplist",
    "hash-ziplist",
    "quicklist",
    "stream"
};

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127.0.0.1:6379>  ZADD page_rank 9 baidu.com 8 bing.com
(integer) 2
127.0.0.1:6379> ZADD page_rank 10 google.com
(integer) 0
127.0.0.1:6379> ZRANGE page_rank 0 -1 WITHSCORES
1) "bing.com"
2) "8"
3) "baidu.com"
4) "9"
5) "google.com"
6) "10"

127.0.0.1:6379> type page_rank
zset
object encoding page_rank
"ziplist"

    
127.0.0.1:6379> ZADD page_rank 2.0 oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo
(integer) 1
127.0.0.1:6379> type page_rank
zset
object encoding page_rank
"skiplist"
    
 ############################### ADVANCED CONFIG ###############################

# Hashes are encoded using a memory efficient data structure when they have a
# small number of entries, and the biggest entry does not exceed a given
# threshold. These thresholds can be configured using the following directives.
hash-max-ziplist-entries 512
hash-max-ziplist-value 64

# Lists are also encoded in a special way to save a lot of space.
# The number of entries allowed per internal list node can be specified
# as a fixed maximum size or a maximum number of elements.
# For a fixed maximum size, use -5 through -1, meaning:
# -5: max size: 64 Kb  <-- not recommended for normal workloads
# -4: max size: 32 Kb  <-- not recommended
# -3: max size: 16 Kb  <-- probably not recommended
# -2: max size: 8 Kb   <-- good
# -1: max size: 4 Kb   <-- good
# Positive numbers mean store up to _exactly_ that number of elements
# per list node.
# The highest performing option is usually -2 (8 Kb size) or -1 (4 Kb size),
# but if your use case is unique, adjust the settings as necessary.
list-max-ziplist-size -2


# Sets have a special encoding in just one case: when a set is composed
# of just strings that happen to be integers in radix 10 in the range
# of 64 bit signed integers.
# The following configuration setting sets the limit in the size of the
# set in order to use this special memory saving encoding.
set-max-intset-entries 512

# Similarly to hashes and lists, sorted sets are also specially encoded in
# order to save a lot of space. This encoding is only used when the length and
# elements of a sorted set are below the following limits:
zset-max-ziplist-entries 128
zset-max-ziplist-value 64

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The ziplist is a specially encoded dually linked list that is designed
 * to be very memory efficient. It stores both strings and integer values,
 * where integers are encoded as actual integers instead of a series of
 * characters. It allows push and pop operations on either side of the list
 * in O(1) time. However, because every operation requires a reallocation of
 * the memory used by the ziplist, the actual complexity is related to the
 * amount of memory used by the ziplist.
     
  ziplist是一个经过特殊编码的双向链表，它的设计目标就是为了提高存储效率。ziplist可以用于存储字符串或整数，其中整数是按真正的二进制表示进行编码的，而不是编码成字符串序列。它能以O(1)的时间复杂度在表的两端提供push和pop操作。

实际上，ziplist充分体现了Redis对于存储效率的追求。一个普通的双向链表，链表中每一项都占用独立的一块内存，各项之间用地址指针（或引用）连接起来。这种方式会带来大量的内存碎片，而且地址指针也会占用额外的内存。
  
     而ziplist却是将表中每一项存放在前后连续的地址空间内，一个ziplist整体占用一大块内存。它是一个表（list），但其实不是一个链表（linked list）。

另外，ziplist为了在细节上节省内存，对于值的存储采用了变长的编码方式，大概意思是说，对于大的整数，就多用一些字节来存储，而对于小的整数，就少用一些字节来存储。我们接下来很快就会讨论到这些实现细节

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file :t_zset.c
    
    
typedef struct zset {
  dict *dict;//无需排列，单key查找
  zskiplist *zsl; //有序排列，范围查找
} zset;

typedef struct zskiplist {
  struct zskiplistNode *header, *tail;
  unsigned long length;
  int level; //tree的最大高度。
} 
typedef struct zskiplistNode {
  sds ele;                        //内容
  double score;                   //排序分值
  struct zskiplistNode *backward; //后面
  struct zskiplistLevel {
    struct zskiplistNode *forward;
    unsigned long span;
  } level[]; //前面
} zskiplistNode;

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127.0.0.1:6379> sadd numbers 1 2 3 4
(integer) 4
127.0.0.1:6379> object encoding numbers
"intset"

127.0.0.1:6379> sadd numbers 1111111111111111111111111111111111111111111111111111
(integer) 1
127.0.0.1:6379> object encoding numbers
"hashtable"

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         +----+
         | M1 |
         | S1 | <- C1 (writes will be lost)
         +----+
            |
            /
            /
+------+    |    +----+
| [M2] |----+----| R3 |
| S2   |         | S3 |
+------+         +----+

# It is possible for a master to stop accepting writes if there are less than
# N replicas connected, having a lag less or equal than M seconds.
#
# The N replicas need to be in "online" state.
#
# The lag in seconds, that must be <= the specified value, is calculated from
# the last ping received from the replica, that is usually sent every second.
#
# This option does not GUARANTEE that N replicas will accept the write, but
# will limit the window of exposure for lost writes in case not enough replicas
# are available, to the specified number of seconds.
#
# For example to require at least 3 replicas with a lag <= 10 seconds use:
#
# min-replicas-to-write 3
# min-replicas-max-lag 10
#

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/* Context for an async connection to Redis */
typedef struct redisAsyncContext {
    /* Hold the regular context, so it can be realloc'ed. */
    redisContext c;

    /* Setup error flags so they can be used directly. */
    int err;
    char *errstr;

    /* Not used by hiredis */
    void *data;
    void (*dataHandler)(struct redisAsyncContext* ac);

    /* Event library data and hooks */
    struct {
        void *data;

        /* Hooks that are called when the library expects to start
         * reading/writing. These functions should be idempotent. */
        void (*addRead)(void *privdata);
        void (*delRead)(void *privdata);
        void (*addWrite)(void *privdata);
        void (*delWrite)(void *privdata);
        void (*cleanup)(void *privdata);
    } ev;

    /* Called when either the connection is terminated due to an error or per
     * user request. The status is set accordingly (REDIS_OK, REDIS_ERR). */
    redisDisconnectCallback *onDisconnect;

    /* Called when the first write event was received. */
    redisConnectCallback *onConnect;

    /* Regular command callbacks */
    redisCallbackList replies;

    /* Subscription callbacks */
    struct {
        redisCallbackList invalid;
        struct dict *channels;
        struct dict *patterns;
    } sub;
} redisAsyncContext;



class dns_down_getredis_time:public I_redis_connect
{
     //single_instance 
	 redisAsyncContext   * m_redisAsynHandler;
	 redisContext        *m_redisHandler;
}
//资源隔离
void  dns_down_redisconnect_mgr::start_new_redis(string &_strRedisIP, int _iRedisPort, string & _strAppName, int daIndex, int dropTimeout)
{
	//不同的资源
    if (_RedisHandler)
    {
		_RedisHandler->start(_strRedisIP.c_str(), _iRedisPort, _strAppName, daIndex, dropTimeout);
        //资源的管理
		m_MapredisConnectMgr[_strAppName] = _RedisHandler;

    }
}

void dns_down_getredis_time::start(const char *_redisIP, int _iRedisPort, string &_strAppName, int dbIndex, int dropTimeout)
{
	connect_redis_server(_redisIP, _iRedisPort);
}

int dns_down_getredis_time::connect_redis_server(const char *_redisIP, int _iRedisPort)
{
	asyn_connect_redis_server(_redisIP, _iRedisPort);
	return 0;

}
// 挖矿
int  dns_down_getredis_time::asyn_connect_redis_server(const char *_redisIP, int _iRedisPort)
{
	m_redisAsynHandler = redisAsyncConnect(_redisIP, _iRedisPort);
	m_redisAsynHandler->data = this;
 
	if (NULL == dns_down_getredis_time::ae_loop)
	{
		ae_loop = aeCreateEventLoop(64);
	}

 
	redisAeAttach(ae_loop, m_redisAsynHandler);
    //
	redisAsyncSetConnectCallback(m_redisAsynHandler, connectCallback);
	redisAsyncSetDisconnectCallback(m_redisAsynHandler, disconnectCallback);
	//asyn
	
	//this is a loop
	static pthread_t  tid = NULL;
	if (NULL == tid)
	{   
	  
		pthread_create(&tid, NULL, thread_event_run, NULL);
		
	}

}
//切换到指定的数据库
void connectCallback(const redisAsyncContext *c, int status) {

	dns_down_getredis_time *pthis = (dns_down_getredis_time *)c->data;
	if (pthis->m_redisAsynHandler)
	{
		redisAsyncCommand(pthis->m_redisAsynHandler, select_callback, NULL, "SELECT %d", pthis->m_dbIndex);

		REDIS_LOG_HEAD_FORTHREAD << "connect redis by asyn suc!";
	}
	

}


//订阅模式

void subCallback(redisAsyncContext *c, void *r, void *priv)
{
	dns_down *pthis = (dns_down*)c->data;

	redisReply *_reply = (redisReply *)r;
	char * _chFlag = (char *)priv;

	if (_reply->type == REDIS_REPLY_ARRAY && _reply->elements == 3)//sub
    {
		REDIS_LOG_HEAD_FORTHREAD << "get sub msg  channel: " << _reply->element[1]->str
			<< " context: " << _reply->element[2]->str << " flag: " << _reply->element[0]->str;


}
https://github.com/redis/hiredis/issues/55