读<<Redis设计与实现>>与redis(5.0)源码__对象

redisObject

typedef struct redisObject {
    unsigned type:4; // 类型,4位
    unsigned encoding:4; // 编码
    // 上次访问时间
    // #define LRU_BITS 24
    unsigned lru:LRU_BITS; /* LRU time (relative to global lru_clock) or
                            * LFU data (least significant 8 bits frequency
                            * and most significant 16 bits access time). */
    int refcount; // 引用次数
    void *ptr;    // 底层地址
} robj;

• type类型

  #define OBJ_STRING 0    /* String object. */
  #define OBJ_LIST 1      /* List object. */
  #define OBJ_SET 2       /* Set object. */
  #define OBJ_ZSET 3      /* Sorted set object. */
  #define OBJ_HASH 4      /* Hash object. */
  #define OBJ_MODULE 5    /* Module object. */,Redis module 直接管理的
  #define OBJ_STREAM 6    /* Stream object. */

• encoding编码

  #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 */ 主要在rdb里面使用
  #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 */

t_string

1. 有三种编码方式,OBJ_ENCODING_INT,OBJ_ENCODING_EMBSTR,OBJ_ENCODING_RAW
2. OBJ_ENCODING_EMBSTR_SIZE_LIMIT = 44,也就是小于等于44子长用embstr编码,大于就用raw.因为redisObject大小 = (4+4+24)/8+4+8 = 16,sdshdr8除去buf外的大小是3(len,alloc,flag),预留1byte的’\0’,供20byte.redis的内存分配方法按2^n分配,所以最接近的是64,剩下44byte.
3. tryObjectEncoding

   /* Try to encode a string object in order to save space */
   robj *tryObjectEncoding(robj *o) {
       long value;
       sds s = o->ptr;
       size_t len;
   
       /* Make sure this is a string object, the only type we encode
        * in this function. Other types use encoded memory efficient
        * representations but are handled by the commands implementing
        * the type. */
       serverAssertWithInfo(NULL,o,o->type == OBJ_STRING);
   
       /* We try some specialized encoding only for objects that are
        * RAW or EMBSTR encoded, in other words objects that are still
        * in represented by an actually array of chars. */
       if (!sdsEncodedObject(o)) return o;
   
       /* It's not safe to encode shared objects: shared objects can be shared
        * everywhere in the "object space" of Redis and may end in places where
        * they are not handled. We handle them only as values in the keyspace. */
        if (o->refcount > 1) return o;
   
       /* Check if we can represent this string as a long integer.
        * Note that we are sure that a string larger than 20 chars is not
        * representable as a 32 nor 64 bit integer. */
       len = sdslen(s);
       // 20减去4个长度剩下16,2^64~=1.84E19(所以超过20位,减去符号19位,超过了int64表示的极限)
       if (len <= 20 && string2l(s,len,&value)) { // 是整数
           /* This object is encodable as a long. Try to use a shared object.
            * Note that we avoid using shared integers when maxmemory is used
            * because every object needs to have a private LRU field for the LRU
            * algorithm to work well. */
            // 如果设置了最大使用内存,说明要进行回收,不能有共享变量(要LRU)
           if ((server.maxmemory == 0 ||
               !(server.maxmemory_policy & MAXMEMORY_FLAG_NO_SHARED_INTEGERS)) &&
               value >= 0 &&
               value < OBJ_SHARED_INTEGERS)
           {
               decrRefCount(o);
               incrRefCount(shared.integers[value]);
               return shared.integers[value];
           } else {
               if (o->encoding == OBJ_ENCODING_RAW) sdsfree(o->ptr);
               o->encoding = OBJ_ENCODING_INT;
               o->ptr = (void*) value;
               return o;
           }
       }
   
       /* If the string is small and is still RAW encoded,
        * try the EMBSTR encoding which is more efficient.
        * In this representation the object and the SDS string are allocated
        * in the same chunk of memory to save space and cache misses. */
        // 如果小于等于44,改用EMBSTR
        // 说明默认是RAW编码
       if (len <= OBJ_ENCODING_EMBSTR_SIZE_LIMIT) {
           robj *emb;
   
           if (o->encoding == OBJ_ENCODING_EMBSTR) return o;
           emb = createEmbeddedStringObject(s,sdslen(s));
           decrRefCount(o);
           return emb;
       }
   
       /* We can't encode the object...
        *
        * Do the last try, and at least optimize the SDS string inside
        * the string object to require little space, in case there
        * is more than 10% of free space at the end of the SDS string.
        *
        * We do that only for relatively large strings as this branch
        * is only entered if the length of the string is greater than
        * OBJ_ENCODING_EMBSTR_SIZE_LIMIT. */
       trimStringObjectIfNeeded(o);
   
       /* Return the original object. */
       return o;
   }

t_list

1. 编码方式有OBJ_ENCODING_QUICKLIST(OBJ_ENCODING_LINKEDLIST被弃用)(,OBJ_ENCODING_ZIPLIST在list里没用了)
2. quicklist

• 将linkedlist和ziplist混合起来使用,每个节点是一个ziplist
• list-max-ziplist-size设置ziplist的大小,正数表示长度,负数表示 -n = 2^(n+1)kb

t_hash

1. 编码方式有OBJ_ENCODING_ZIPLIST,OBJ_ENCODING_HT
2. 如果长度大于server.hash_max_ziplist_entries,转换成OBJ_ENCODING_HT
3. 如果键值的长度大于 server.hash_max_ziplist_value,转换成OBJ_ENCODING_HT

t_set

1. 编码方式有OBJ_ENCODING_HT,OBJ_ENCODING_INTSET
2. 如果长度大于server.set_max_intset_entries,或者有非整数,转换成OBJ_ENCODING_HT

t_zset

1. 编码方式有OBJ_ENCODING_ZIPLIST,OBJ_ENCODING_SKIPLIST
2. 如果长度大于server.zset_max_ziplist_entries,或者有非整数,转换成OBJ_ENCODING_SKIPLIST
3. 如果值的长度大于 server.zset_max_ziplist_value,转换成OBJ_ENCODING_SKIPLIST