Redis作为nosql数据库，kv string型数据的支持是最基础的，但是如果仅有kv的操作，也不至于有redis的成功。（memcache就是个例子）
Redis除了string, 还有hash,list,set,zset。
所以，我们就来看看hash的相关操作实现吧。
首先，我们从作用上理解hash存在的意义：Redis hash 是一个 string 类型的 field 和 value 的映射表，hash 特别适合用于存储对象。从另一个方面来说是，hash可以聚合很多类似的属性，这是string中难以实现的。
所以，总体来说，hash的命令与string的命令差不太多。其操作手册如下：
1> hdel 命令：删除一个或多个哈希表字段
格式：HDEL key field2 [field2]
返回值：被成功删除字段的数量，不包括被忽略的字段。2> hexists 命令：查看哈希表 key 中，指定的字段是否存在
格式：HEXISTS key field
返回值：如果哈希表含有给定字段，返回 1 。 如果哈希表不含有给定字段，或 key 不存在，返回 0 。3> hget 命令：获取存储在哈希表中指定字段的值
格式：HGET key field
返回值：返回给定字段的值。如果给定的字段或 key 不存在时，返回 nil 。4> hgetall 命令：获取在哈希表中指定 key 的所有字段和值
格式：HGETALL key
返回值：以列表形式返回哈希表的字段及字段值。 若 key 不存在，返回空列表。5> hincrby 命令：为哈希表 key 中的指定字段的整数值加上增量 increment
格式：HINCRBY key field increment
返回值：执行 HINCRBY 命令之后，哈希表中字段的值。6> hincrbyfloat 命令：为哈希表 key 中的指定字段的浮点数值加上增量 increment
格式：HINCRBYFLOAT key field increment
返回值：执行 Hincrbyfloat 命令之后，哈希表中字段的值。7> hkeys 命令：获取所有哈希表中的字段
格式：HKEYS key
返回值：包含哈希表中所有字段的列表。 当 key 不存在时，返回一个空列表。8> hlen 命令：获取哈希表中字段的数量
格式：HLEN key
返回值：哈希表中字段的数量。 当 key 不存在时，返回 0 。9> hmget 命令：获取所有给定字段的值
格式：HMGET key field1 [field2]
返回值：一个包含多个给定字段关联值的表，表值的排列顺序和指定字段的请求顺序一样。10> hmset 命令：同时将多个 field-value (域-值)对设置到哈希表 key 中
格式：HMSET key field1 value1 [field2 value2 ]
返回值：如果命令执行成功，返回 OK 。11> hset 命令：将哈希表 key 中的字段 field 的值设为 value
格式：HSET key field value
返回值：如果字段是哈希表中的一个新建字段，并且值设置成功，返回 1 。 如果哈希表中域字段已经存在且旧值已被新值覆盖，返回 0 。12> hsetnx 命令：只有在字段 field 不存在时，设置哈希表字段的值
格式：HSETNX key field value
返回值：设置成功，返回 1 。 如果给定字段已经存在且没有操作被执行，返回 0 。13> hvals 命令：获取哈希表中所有值
格式：HVALS key
返回值：一个包含哈希表中所有值的表。 当 key 不存在时，返回一个空表。14> hscan 命令：迭代哈希表中的键值对
格式：HSCAN key cursor [MATCH pattern] [COUNT count]
其中，有的是单kv操作有的是指量操作，有的是写操作有的是读操作。从实现上看，大体上很多命令是类似的:
比如： hset/hmset/hincrbyXXX 可以是一类的
比如：hget/hgetall/hexists/hkeys/hmget 可以是一类
注意：以上分法仅是为了让我们看清本质，对实际使用并无实际参考意义。
所以，我们就挑几个方法来解析下 hash 的操作实现吧。
零、hash数据结构
hash相关的命令定义如下：
{"hset",hsetCommand,,"wmF",,NULL,,,,,},
{"hsetnx",hsetnxCommand,,"wmF",,NULL,,,,,},
{"hget",hgetCommand,,"rF",,NULL,,,,,},
{"hmset",hmsetCommand,-,"wm",,NULL,,,,,},
{"hmget",hmgetCommand,-,"r",,NULL,,,,,},
{"hincrby",hincrbyCommand,,"wmF",,NULL,,,,,},
{"hincrbyfloat",hincrbyfloatCommand,,"wmF",,NULL,,,,,},
{"hdel",hdelCommand,-,"wF",,NULL,,,,,},
{"hlen",hlenCommand,,"rF",,NULL,,,,,},
{"hstrlen",hstrlenCommand,,"rF",,NULL,,,,,},
{"hkeys",hkeysCommand,,"rS",,NULL,,,,,},
{"hvals",hvalsCommand,,"rS",,NULL,,,,,},
{"hgetall",hgetallCommand,,"r",,NULL,,,,,},
{"hexists",hexistsCommand,,"rF",,NULL,,,,,},
{"hscan",hscanCommand,-,"rR",,NULL,,,,,},
ziplist 数据结构
typedef struct zlentry {
unsigned int prevrawlensize, prevrawlen;
unsigned int lensize, len;
unsigned int headersize;
unsigned char encoding;
unsigned char *p;
} zlentry;
#define ZIPLIST_BYTES(zl) (*((uint32_t*)(zl)))
#define ZIPLIST_TAIL_OFFSET(zl) (*((uint32_t*)((zl)+sizeof(uint32_t))))
#define ZIPLIST_LENGTH(zl) (*((uint16_t*)((zl)+sizeof(uint32_t)*2)))
#define ZIPLIST_HEADER_SIZE (sizeof(uint32_t)*2+sizeof(uint16_t))
#define ZIPLIST_END_SIZE (sizeof(uint8_t))
#define ZIPLIST_ENTRY_HEAD(zl) ((zl)+ZIPLIST_HEADER_SIZE)
#define ZIPLIST_ENTRY_TAIL(zl) ((zl)+intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl)))
#define ZIPLIST_ENTRY_END(zl) ((zl)+intrev32ifbe(ZIPLIST_BYTES(zl))-1)
hashtable 数据结构：
typedef struct dict {
dictType *type;
void *privdata;
dictht ht[];
long rehashidx; /* rehashing not in progress if rehashidx == -1 */
unsigned long iterators; /* number of iterators currently running */
} dict;
typedef struct dictht {
dictEntry **table;
unsigned long size;
unsigned long sizemask;
unsigned long used;
} dictht;
typedef struct dictEntry {
void *key;
void *val;
struct dictEntry *next;
} dictEntry;
一、hset 设置单个 field -> value
“增删改查”中的“增改” 就是它了。
// t_hash.c, set key field value
void hsetCommand(client *c) {
int update;
robj *o;
// 1. 查找hash的key是否存在，不存在则新建一个，然后在其上进行数据操作
if ((o = hashTypeLookupWriteOrCreate(c,c->argv[])) == NULL) return;
// 2. 检查2-3个参数是否需要将简单版（ziplist）hash表转换为复杂的hash表，转换后的表通过 o->ptr 体现
hashTypeTryConversion(o,c->argv,,);
// 3. 添加kv到 o 的hash表中
update = hashTypeSet(o,c->argv[]->ptr,c->argv[]->ptr,HASH_SET_COPY);
addReply(c, update ? shared.czero : shared.cone);
// 变更命令传播
signalModifiedKey(c->db,c->argv[]);
notifyKeyspaceEvent(NOTIFY_HASH,"hset",c->argv[],c->db->id);
server.dirty++;
} // 1. 获取db外部的key, 即整体hash数据实例
// t_hash.c
robj *hashTypeLookupWriteOrCreate(client *c, robj *key) {
robj *o = lookupKeyWrite(c->db,key);
if (o == NULL) {
// 此处创建的hashObject是以 ziplist 形式的
o = createHashObject();
dbAdd(c->db,key,o);
} else {
// 不是hash类型的键已存在，不可覆盖，返回错误
if (o->type != OBJ_HASH) {
addReply(c,shared.wrongtypeerr);
return NULL;
}
}
return o;
}
// object.c, 创建hashObject, 以 ziplist 形式创建
robj *createHashObject(void) {
unsigned char *zl = ziplistNew();
robj *o = createObject(OBJ_HASH, zl);
o->encoding = OBJ_ENCODING_ZIPLIST;
return o;
}
// ziplist.c
static unsigned char *createList() {
unsigned char *zl = ziplistNew();
zl = ziplistPush(zl, (unsigned char*)"foo", , ZIPLIST_TAIL);
zl = ziplistPush(zl, (unsigned char*)"quux", , ZIPLIST_TAIL);
zl = ziplistPush(zl, (unsigned char*)"hello", , ZIPLIST_HEAD);
zl = ziplistPush(zl, (unsigned char*)"", , ZIPLIST_TAIL);
return zl;
} // 2. 检查参数，是否需要将 ziplist 形式的hash表转换为真正的hash表
/* Check the length of a number of objects to see if we need to convert a
* ziplist to a real hash. Note that we only check string encoded objects
* as their string length can be queried in constant time. */
void hashTypeTryConversion(robj *o, robj **argv, int start, int end) {
int i; if (o->encoding != OBJ_ENCODING_ZIPLIST) return; for (i = start; i <= end; i++) {
// 参数大于设置的 hash_max_ziplist_value (默认: 64)时，会直接将 ziplist 转换为 ht
// OBJ_ENCODING_RAW, OBJ_ENCODING_EMBSTR
// 循环检查参数，只要发生了一次转换就结束检查（没必要继续了）
if (sdsEncodedObject(argv[i]) &&
sdslen(argv[i]->ptr) > server.hash_max_ziplist_value)
{
// 这个转换过程很有意思，我们深入看看
hashTypeConvert(o, OBJ_ENCODING_HT);
break;
}
}
}
// t_hash.c, 转换编码方式 (如上, ziplist -> ht)
void hashTypeConvert(robj *o, int enc) {
if (o->encoding == OBJ_ENCODING_ZIPLIST) {
// 此处我们只处理这种情况
hashTypeConvertZiplist(o, enc);
} else if (o->encoding == OBJ_ENCODING_HT) {
serverPanic("Not implemented");
} else {
serverPanic("Unknown hash encoding");
}
}
// t_hash.c, 转换编码 ziplist 为目标 enc (实际只能是 OBJ_ENCODING_HT)
void hashTypeConvertZiplist(robj *o, int enc) {
serverAssert(o->encoding == OBJ_ENCODING_ZIPLIST); if (enc == OBJ_ENCODING_ZIPLIST) {
/* Nothing to do... */ } else if (enc == OBJ_ENCODING_HT) {
hashTypeIterator *hi;
dict *dict;
int ret;
// 迭代器创建
hi = hashTypeInitIterator(o);
// 一个hash的数据结构就是一个 dict, 从这个级别来说, hash 与 db 是一个级别的
dict = dictCreate(&hashDictType, NULL);
// 依次迭代 o, 赋值到 hi->fptr, hi->vptr
// 依次添加到 dict 中
while (hashTypeNext(hi) != C_ERR) {
sds key, value;
// 从 hi->fptr 中获取key
// 从 hi->vptr 中获取value
key = hashTypeCurrentObjectNewSds(hi,OBJ_HASH_KEY);
value = hashTypeCurrentObjectNewSds(hi,OBJ_HASH_VALUE);
// 添加到 dict 中
ret = dictAdd(dict, key, value);
if (ret != DICT_OK) {
serverLogHexDump(LL_WARNING,"ziplist with dup elements dump",
o->ptr,ziplistBlobLen(o->ptr));
serverPanic("Ziplist corruption detected");
}
}
// 释放迭代器
hashTypeReleaseIterator(hi);
zfree(o->ptr);
// 将变更反映到o对象上返回
o->encoding = OBJ_ENCODING_HT;
o->ptr = dict;
} else {
serverPanic("Unknown hash encoding");
}
}
// 2.1. 迭代ziplist元素
// t_hash.c, 迭代器
/* Move to the next entry in the hash. Return C_OK when the next entry
* could be found and C_ERR when the iterator reaches the end. */
int hashTypeNext(hashTypeIterator *hi) {
if (hi->encoding == OBJ_ENCODING_ZIPLIST) {
unsigned char *zl;
unsigned char *fptr, *vptr;
// 每次都是基于原始字符器进行计算偏移
// 迭代的是 fptr,vptr
zl = hi->subject->ptr;
fptr = hi->fptr;
vptr = hi->vptr;
// 第一次查找时使用index查找，后续则使用 fptr,vptr 进行迭代
if (fptr == NULL) {
/* Initialize cursor */
serverAssert(vptr == NULL);
fptr = ziplistIndex(zl, );
} else {
/* Advance cursor */
serverAssert(vptr != NULL);
fptr = ziplistNext(zl, vptr);
}
if (fptr == NULL) return C_ERR; /* Grab pointer to the value (fptr points to the field) */
vptr = ziplistNext(zl, fptr);
serverAssert(vptr != NULL); /* fptr, vptr now point to the first or next pair */
hi->fptr = fptr;
hi->vptr = vptr;
} else if (hi->encoding == OBJ_ENCODING_HT) {
if ((hi->de = dictNext(hi->di)) == NULL) return C_ERR;
} else {
serverPanic("Unknown hash encoding");
}
return C_OK;
}
// ziplist.c, 查找 index 的元素
/* Returns an offset to use for iterating with ziplistNext. When the given
* index is negative, the list is traversed back to front. When the list
* doesn't contain an element at the provided index, NULL is returned. */
unsigned char *ziplistIndex(unsigned char *zl, int index) {
unsigned char *p;
unsigned int prevlensize, prevlen = ;
if (index < ) {
// 小于0时，反向查找
index = (-index)-;
p = ZIPLIST_ENTRY_TAIL(zl);
if (p[] != ZIP_END) {
ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
while (prevlen > && index--) {
p -= prevlen;
ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
}
}
} else {
p = ZIPLIST_ENTRY_HEAD(zl);
while (p[] != ZIP_END && index--) {
p += zipRawEntryLength(p);
}
}
// 迭代完成还没找到元素 p[0]=ZIP_END
// index 超出整体ziplist大小则遍历完成后 index>0
return (p[] == ZIP_END || index > ) ? NULL : p;
}
// ziplist.c, 由 fptr,vptr 进行迭代元素
/* Return pointer to next entry in ziplist.
*
* zl is the pointer to the ziplist
* p is the pointer to the current element
*
* The element after 'p' is returned, otherwise NULL if we are at the end. */
unsigned char *ziplistNext(unsigned char *zl, unsigned char *p) {
((void) zl); /* "p" could be equal to ZIP_END, caused by ziplistDelete,
* and we should return NULL. Otherwise, we should return NULL
* when the *next* element is ZIP_END (there is no next entry). */
if (p[] == ZIP_END) {
return NULL;
}
// 当前指针偏移当前元素长度（根据ziplist协议），即到下一元素指针位置
p += zipRawEntryLength(p);
if (p[] == ZIP_END) {
return NULL;
} return p;
}
/* Return the total number of bytes used by the entry pointed to by 'p'. */
static unsigned int zipRawEntryLength(unsigned char *p) {
unsigned int prevlensize, encoding, lensize, len;
ZIP_DECODE_PREVLENSIZE(p, prevlensize);
ZIP_DECODE_LENGTH(p + prevlensize, encoding, lensize, len);
return prevlensize + lensize + len;
} // 2.2. t_hash.c, 获取 hashTypeIterator 的具体值，写入 vstr, vlen 中
/* Return the key or value at the current iterator position as a new
* SDS string. */
sds hashTypeCurrentObjectNewSds(hashTypeIterator *hi, int what) {
unsigned char *vstr;
unsigned int vlen;
long long vll; hashTypeCurrentObject(hi,what,&vstr,&vlen,&vll);
if (vstr) return sdsnewlen(vstr,vlen);
return sdsfromlonglong(vll);
}
/* Higher level function of hashTypeCurrent*() that returns the hash value
* at current iterator position.
*
* The returned element is returned by reference in either *vstr and *vlen if
* it's returned in string form, or stored in *vll if it's returned as
* a number.
*
* If *vll is populated *vstr is set to NULL, so the caller
* can always check the function return by checking the return value
* type checking if vstr == NULL. */
void hashTypeCurrentObject(hashTypeIterator *hi, int what, unsigned char **vstr, unsigned int *vlen, long long *vll) {
if (hi->encoding == OBJ_ENCODING_ZIPLIST) {
*vstr = NULL;
hashTypeCurrentFromZiplist(hi, what, vstr, vlen, vll);
} else if (hi->encoding == OBJ_ENCODING_HT) {
sds ele = hashTypeCurrentFromHashTable(hi, what);
*vstr = (unsigned char*) ele;
*vlen = sdslen(ele);
} else {
serverPanic("Unknown hash encoding");
}
} // t_hash.c, 从ziplist中获取某个 hashTypeIterator 的具体值，结果定稿 vstr, vlen
/* Get the field or value at iterator cursor, for an iterator on a hash value
* encoded as a ziplist. Prototype is similar to `hashTypeGetFromZiplist`. */
void hashTypeCurrentFromZiplist(hashTypeIterator *hi, int what,
unsigned char **vstr,
unsigned int *vlen,
long long *vll)
{
int ret; serverAssert(hi->encoding == OBJ_ENCODING_ZIPLIST);
// OBJ_HASH_KEY 从 fptr 中获取, 否则从 vptr 中获取
if (what & OBJ_HASH_KEY) {
ret = ziplistGet(hi->fptr, vstr, vlen, vll);
serverAssert(ret);
} else {
ret = ziplistGet(hi->vptr, vstr, vlen, vll);
serverAssert(ret);
}
}
// ziplist.c,
/* Get entry pointed to by 'p' and store in either '*sstr' or 'sval' depending
* on the encoding of the entry. '*sstr' is always set to NULL to be able
* to find out whether the string pointer or the integer value was set.
* Return 0 if 'p' points to the end of the ziplist, 1 otherwise. */
unsigned int ziplistGet(unsigned char *p, unsigned char **sstr, unsigned int *slen, long long *sval) {
zlentry entry;
if (p == NULL || p[] == ZIP_END) return ;
if (sstr) *sstr = NULL;
// 按照ziplist的编码协议, 获取头部信息
zipEntry(p, &entry);
if (ZIP_IS_STR(entry.encoding)) {
if (sstr) {
*slen = entry.len;
*sstr = p+entry.headersize;
}
} else {
if (sval) {
*sval = zipLoadInteger(p+entry.headersize,entry.encoding);
}
}
return ;
}
// ziplist.c, 解析原始字符串为 zlentry
/* Return a struct with all information about an entry. */
static void zipEntry(unsigned char *p, zlentry *e) {
// 按照ziplist的编码协议,依次读取 prevrawlensize, prevrawlen
ZIP_DECODE_PREVLEN(p, e->prevrawlensize, e->prevrawlen);
// 指向下一位置偏移，按照ziplist的编码协议,依次读取 encoding, lensize, len
ZIP_DECODE_LENGTH(p + e->prevrawlensize, e->encoding, e->lensize, e->len);
// 除去header得到 body偏移
e->headersize = e->prevrawlensize + e->lensize;
e->p = p;
}
具体header解析如下, 有兴趣的点开瞅瞅:
// ziplist.c
/* Decode the length of the previous element, from the perspective of the entry
* pointed to by 'ptr'. */
#define ZIP_DECODE_PREVLEN(ptr, prevlensize, prevlen) do { \
// 解析第1个字符为 prevlensize
ZIP_DECODE_PREVLENSIZE(ptr, prevlensize); \
if ((prevlensize) == ) { \
(prevlen) = (ptr)[]; \
} else if ((prevlensize) == ) { \
assert(sizeof((prevlensize)) == ); \
// 当ptr[0]>254时，代表内容有点大，需要使用 5个字符保存上一字符长度
memcpy(&(prevlen), ((char*)(ptr)) + , ); \
memrev32ifbe(&prevlen); \
} \
} while();
/* Decode the number of bytes required to store the length of the previous
* element, from the perspective of the entry pointed to by 'ptr'. */
#define ZIP_DECODE_PREVLENSIZE(ptr, prevlensize) do { \
if ((ptr)[] < ZIP_BIGLEN) { \
(prevlensize) = ; \
} else { \
(prevlensize) = ; \
} \
} while();
/* Decode the length encoded in 'ptr'. The 'encoding' variable will hold the
* entries encoding, the 'lensize' variable will hold the number of bytes
* required to encode the entries length, and the 'len' variable will hold the
* entries length. */
#define ZIP_DECODE_LENGTH(ptr, encoding, lensize, len) do { \
// 解析第1个字符为 编码格式 &ZIP_STR_MASK=0xc0
ZIP_ENTRY_ENCODING((ptr), (encoding)); \
if ((encoding) < ZIP_STR_MASK) { \
// 0 << 6 =0
// 具体解析如下代码,
if ((encoding) == ZIP_STR_06B) { \
(lensize) = ; \
(len) = (ptr)[] & 0x3f; \
}
// 1 << 6 =64
else if ((encoding) == ZIP_STR_14B) { \
(lensize) = ; \
(len) = (((ptr)[] & 0x3f) << ) | (ptr)[]; \
}
// 2 << 6 =128
else if (encoding == ZIP_STR_32B) { \
(lensize) = ; \
(len) = ((ptr)[] << ) | \
((ptr)[] << ) | \
((ptr)[] << ) | \
((ptr)[]); \
} else { \
assert(NULL); \
} \
} else { \
// 超过 0xc0 的长度了，直接使用 1,2,3,4 表示len
(lensize) = ; \
(len) = zipIntSize(encoding); \
} \
} while();
/* Extract the encoding from the byte pointed by 'ptr' and set it into
* 'encoding'. */
#define ZIP_ENTRY_ENCODING(ptr, encoding) do { \
(encoding) = (ptr[]); \
if ((encoding) < ZIP_STR_MASK) (encoding) &= ZIP_STR_MASK; \
} while() /* Different encoding/length possibilities */
#define ZIP_STR_MASK 0xc0
#define ZIP_INT_MASK 0x30
#define ZIP_STR_06B (0 << 6) // 0x00
#define ZIP_STR_14B (1 << 6) // 0x40
#define ZIP_STR_32B (2 << 6) // 0x80
#define ZIP_INT_16B (0xc0 | 0<<4) // 0xc0
#define ZIP_INT_32B (0xc0 | 1<<4) // 0xd0
#define ZIP_INT_64B (0xc0 | 2<<4) // 0xe0
#define ZIP_INT_24B (0xc0 | 3<<4) // 0xf0
#define ZIP_INT_8B 0xfe // 0xfe
添加kv到对应的key实例中：
// 3. 添加kv到 hash表中, 稍微复杂
// t_hash.c, 做变更到hash表中
int hashTypeSet(robj *o, sds field, sds value, int flags) {
int update = ;
// 针对ziplist 的添加, 与 ht 编码的添加, 自然是分别处理
if (o->encoding == OBJ_ENCODING_ZIPLIST) {
unsigned char *zl, *fptr, *vptr; zl = o->ptr;
// 找到ziplist 的头节点指针
fptr = ziplistIndex(zl, ZIPLIST_HEAD);
if (fptr != NULL) {
// 尝试查找该 field 对应的元素(从1开始)，如果找到则先删除原值，然后统一添加
fptr = ziplistFind(fptr, (unsigned char*)field, sdslen(field), );
if (fptr != NULL) {
/* Grab pointer to the value (fptr points to the field) */
// value 不可以为null, 否则 ziplist 将无法工作
vptr = ziplistNext(zl, fptr);
serverAssert(vptr != NULL);
update = ; /* Delete value */
// 先删除旧的 value, 再以插入的形式更新, 后续讲删除时再详解
zl = ziplistDelete(zl, &vptr); /* Insert new value */
// 重点，将value添加到 ziplist 中
zl = ziplistInsert(zl, vptr, (unsigned char*)value,
sdslen(value));
}
}
// 没有找到对应元素，则直接将元素添加到尾部即可
if (!update) {
/* Push new field/value pair onto the tail of the ziplist */
zl = ziplistPush(zl, (unsigned char*)field, sdslen(field),
ZIPLIST_TAIL);
zl = ziplistPush(zl, (unsigned char*)value, sdslen(value),
ZIPLIST_TAIL);
}
o->ptr = zl; /* Check if the ziplist needs to be converted to a hash table */
// 大于设置的阀值后，转换ziplist为ht(默认: 512)
if (hashTypeLength(o) > server.hash_max_ziplist_entries)
hashTypeConvert(o, OBJ_ENCODING_HT);
} else if (o->encoding == OBJ_ENCODING_HT) {
dictEntry *de = dictFind(o->ptr,field);
if (de) {
sdsfree(dictGetVal(de));
if (flags & HASH_SET_TAKE_VALUE) {
dictGetVal(de) = value;
value = NULL;
} else {
dictGetVal(de) = sdsdup(value);
}
update = ;
} else {
sds f,v;
if (flags & HASH_SET_TAKE_FIELD) {
f = field;
field = NULL;
} else {
f = sdsdup(field);
}
if (flags & HASH_SET_TAKE_VALUE) {
v = value;
value = NULL;
} else {
v = sdsdup(value);
}
dictAdd(o->ptr,f,v);
}
} else {
serverPanic("Unknown hash encoding");
} /* Free SDS strings we did not referenced elsewhere if the flags
* want this function to be responsible. */
if (flags & HASH_SET_TAKE_FIELD && field) sdsfree(field);
if (flags & HASH_SET_TAKE_VALUE && value) sdsfree(value);
return update;
}
// 3.1. 使用ziplist进行保存 field -> value
// ziplist.c, 查找某个 field 是否存在于ziplist中
/* Find pointer to the entry equal to the specified entry. Skip 'skip' entries
* between every comparison. Returns NULL when the field could not be found. */
unsigned char *ziplistFind(unsigned char *p, unsigned char *vstr, unsigned int vlen, unsigned int skip) {
int skipcnt = ;
unsigned char vencoding = ;
long long vll = ; while (p[] != ZIP_END) {
unsigned int prevlensize, encoding, lensize, len;
unsigned char *q;
// 解析整个字符串p的 prevlensize,encoding,lensize,len
ZIP_DECODE_PREVLENSIZE(p, prevlensize);
ZIP_DECODE_LENGTH(p + prevlensize, encoding, lensize, len);
q = p + prevlensize + lensize;
// 传入1, 代表要跳过一个元素, 比如: 查找key时,跳过1个v,然后继续迭代
// 跳过了n个元素后，再从此开始key的比对过程
if (skipcnt == ) {
/* Compare current entry with specified entry */
// 针对不同的编码使用不同的比较方式
if (ZIP_IS_STR(encoding)) {
// 找到相应的元素，直接返回 p 指针
if (len == vlen && memcmp(q, vstr, vlen) == ) {
return p;
}
} else {
/* Find out if the searched field can be encoded. Note that
* we do it only the first time, once done vencoding is set
* to non-zero and vll is set to the integer value. */
if (vencoding == ) {
if (!zipTryEncoding(vstr, vlen, &vll, &vencoding)) {
/* If the entry can't be encoded we set it to
* UCHAR_MAX so that we don't retry again the next
* time. */
vencoding = UCHAR_MAX;
}
/* Must be non-zero by now */
assert(vencoding);
} /* Compare current entry with specified entry, do it only
* if vencoding != UCHAR_MAX because if there is no encoding
* possible for the field it can't be a valid integer. */
if (vencoding != UCHAR_MAX) {
long long ll = zipLoadInteger(q, encoding);
if (ll == vll) {
return p;
}
}
} /* Reset skip count */
// 查找一次，跳过skip次
skipcnt = skip;
} else {
/* Skip entry */
skipcnt--;
} /* Move to next entry */
p = q + len;
} return NULL;
}
// ziplist.c, 添加value到ziplist中
// zl:ziplist实例, p:要插入的key字串, s:要插入的value字串, len:要插入的value的长度
/* Insert an entry at "p". */
unsigned char *ziplistInsert(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {
return __ziplistInsert(zl,p,s,slen);
}
/* Insert item at "p". */
static unsigned char *__ziplistInsert(unsigned char *zl, unsigned char *p, unsigned char *s, unsigned int slen) {
size_t curlen = intrev32ifbe(ZIPLIST_BYTES(zl)), reqlen;
unsigned int prevlensize, prevlen = ;
size_t offset;
int nextdiff = ;
unsigned char encoding = ;
long long value = ; /* initialized to avoid warning. Using a value
that is easy to see if for some reason
we use it uninitialized. */
zlentry tail; /* Find out prevlen for the entry that is inserted. */
if (p[] != ZIP_END) {
ZIP_DECODE_PREVLEN(p, prevlensize, prevlen);
} else {
unsigned char *ptail = ZIPLIST_ENTRY_TAIL(zl);
if (ptail[] != ZIP_END) {
prevlen = zipRawEntryLength(ptail);
}
} /* See if the entry can be encoded */
if (zipTryEncoding(s,slen,&value,&encoding)) {
/* 'encoding' is set to the appropriate integer encoding */
reqlen = zipIntSize(encoding);
} else {
/* 'encoding' is untouched, however zipEncodeLength will use the
* string length to figure out how to encode it. */
reqlen = slen;
}
/* We need space for both the length of the previous entry and
* the length of the payload. */
// 加上prevlen,encoding,slen 的长度，以计算value的存放位置
reqlen += zipPrevEncodeLength(NULL,prevlen);
reqlen += zipEncodeLength(NULL,encoding,slen); /* When the insert position is not equal to the tail, we need to
* make sure that the next entry can hold this entry's length in
* its prevlen field. */
nextdiff = (p[] != ZIP_END) ? zipPrevLenByteDiff(p,reqlen) : ; /* Store offset because a realloc may change the address of zl. */
// 存储当前偏移位置，以便在扩容之后，还能找到相应位置
// p = p -zl + zl
offset = p-zl;
zl = ziplistResize(zl,curlen+reqlen+nextdiff);
p = zl+offset; /* Apply memory move when necessary and update tail offset. */
if (p[] != ZIP_END) {
/* Subtract one because of the ZIP_END bytes */
// 字符拷贝
memmove(p+reqlen,p-nextdiff,curlen-offset-+nextdiff); /* Encode this entry's raw length in the next entry. */
zipPrevEncodeLength(p+reqlen,reqlen); /* Update offset for tail */
ZIPLIST_TAIL_OFFSET(zl) =
intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+reqlen); /* When the tail contains more than one entry, we need to take
* "nextdiff" in account as well. Otherwise, a change in the
* size of prevlen doesn't have an effect on the *tail* offset. */
zipEntry(p+reqlen, &tail);
if (p[reqlen+tail.headersize+tail.len] != ZIP_END) {
ZIPLIST_TAIL_OFFSET(zl) =
intrev32ifbe(intrev32ifbe(ZIPLIST_TAIL_OFFSET(zl))+nextdiff);
}
} else {
/* This element will be the new tail. */
ZIPLIST_TAIL_OFFSET(zl) = intrev32ifbe(p-zl);
} /* When nextdiff != 0, the raw length of the next entry has changed, so
* we need to cascade the update throughout the ziplist */
if (nextdiff != ) {
// 如果本次更新后数据位置变化，则需要更新后续的元素位置
offset = p-zl;
zl = __ziplistCascadeUpdate(zl,p+reqlen);
p = zl+offset;
} /* Write the entry */
// 将 value 写入 p 中, 即写入了 ziplist 中
p += zipPrevEncodeLength(p,prevlen);
p += zipEncodeLength(p,encoding,slen);
if (ZIP_IS_STR(encoding)) {
memcpy(p,s,slen);
} else {
zipSaveInteger(p,value,encoding);
}
ZIPLIST_INCR_LENGTH(zl,);
return zl;
}
// 另外，如果没有旧的元素值时，直接在hash表的末尾添加对应的field->value 即可
// ziplist.c, 在尾部进行添加元素，没有许多的情况要考虑，但是代码完全复用 __ziplistInsert()
unsigned char *ziplistPush(unsigned char *zl, unsigned char *s, unsigned int slen, int where) {
unsigned char *p;
p = (where == ZIPLIST_HEAD) ? ZIPLIST_ENTRY_HEAD(zl) : ZIPLIST_ENTRY_END(zl);
return __ziplistInsert(zl,p,s,slen);
}
鉴于插入过程稍微复杂，咱们画个图重新理一下思路：
看起来没ziplist好像没那么简单呢，为啥还要搞这么复杂呢？其实以上代码，仅是在人看来复杂，对机器来说就是更多的移位计算操作，多消耗点cpu就换来了空间上的节省，是可以的。软件本身的复杂性带来了效益，是软件的价值体现，所以，并非所有的东西都是简单即美。
接下来，我们来看一下使用 HT 的编码又如何存储field->value呢？
// 3.2. OBJ_ENCODING_HT 的 field -> value 的添加
if (o->encoding == OBJ_ENCODING_HT) {
// hash 表中查找对应的 field
dictEntry *de = dictFind(o->ptr,field);
if (de) {
sdsfree(dictGetVal(de));
// hset 时使用 HASH_SET_COPY, 所以直接使用 sdsdup() 即可
if (flags & HASH_SET_TAKE_VALUE) {
dictGetVal(de) = value;
value = NULL;
} else {
dictGetVal(de) = sdsdup(value);
}
update = ;
} else {
// 新增 field -> value
sds f,v;
if (flags & HASH_SET_TAKE_FIELD) {
f = field;
field = NULL;
} else {
f = sdsdup(field);
}
if (flags & HASH_SET_TAKE_VALUE) {
v = value;
value = NULL;
} else {
v = sdsdup(value);
}
// 添加到 hash 表中，前些篇章讲解过，大概就是计算hash，放入v的过程
dictAdd(o->ptr,f,v);
}
}
如此看来，OBJ_ENCODING_HT 的实现反而简单了哦。
总结下 hash的插入过程，hash 初始创建时都是使用ziplist 进行容纳元素的，在特定情况下会触发 ziplist 为 ht 的编码方式, 比如:
1. hset时自身的参数大于设置值(默认: 64)时直接转换 ziplist -> ht;
2. hash表的元素数量大于设置值(默认: 512)时转换 ziplist -> ht;
这么设计的原因是，元素较少且占用空间较小时，使用ziplist会节省空间，且时间消耗与hash表相关并不大，所以 ziplist 是优先的选择了。但是大量数据还是必须要使用hash表存储的。
二、hmset 批量添加元素
hset 和 hmset 在实现上基本如出一辙，所以简单瞅瞅就得了。
// t_hash.c, hmset key f1 v1 f2 v2
void hmsetCommand(client *c) {
int i;
robj *o;
// 参数个数检查，必定是2n
if ((c->argc % ) == ) {
addReplyError(c,"wrong number of arguments for HMSET");
return;
}
// 插入方式与 hset 一毛一样，差别在于批量插入时，会循环向 key-hash表中添加field->value
if ((o = hashTypeLookupWriteOrCreate(c,c->argv[])) == NULL) return;
hashTypeTryConversion(o,c->argv,,c->argc-);
// 循环insert
for (i = ; i < c->argc; i += ) {
hashTypeSet(o,c->argv[i]->ptr,c->argv[i+]->ptr,HASH_SET_COPY);
}
addReply(c, shared.ok);
signalModifiedKey(c->db,c->argv[]);
notifyKeyspaceEvent(NOTIFY_HASH,"hset",c->argv[],c->db->id);
server.dirty++;
}
三、hget 获取某字段值
这种命令的时间复杂度都是 O(1), 所以一般是简单至上。
// t_hash.c
void hgetCommand(client *c) {
robj *o;
// 查找key, 不存在或者类型不一致则直接返回
if ((o = lookupKeyReadOrReply(c,c->argv[],shared.nullbulk)) == NULL ||
checkType(c,o,OBJ_HASH)) return;
// 基于o, 返回 field 对应的元素值即可
addHashFieldToReply(c, o, c->argv[]->ptr);
}
// t_hash.c
static void addHashFieldToReply(client *c, robj *o, sds field) {
int ret; if (o == NULL) {
addReply(c, shared.nullbulk);
return;
} if (o->encoding == OBJ_ENCODING_ZIPLIST) {
unsigned char *vstr = NULL;
unsigned int vlen = UINT_MAX;
long long vll = LLONG_MAX;
// 基于 ziplist,
ret = hashTypeGetFromZiplist(o, field, &vstr, &vlen, &vll);
if (ret < ) {
// 响应为空
addReply(c, shared.nullbulk);
} else {
// 添加到输出缓冲
if (vstr) {
addReplyBulkCBuffer(c, vstr, vlen);
} else {
addReplyBulkLongLong(c, vll);
}
} } else if (o->encoding == OBJ_ENCODING_HT) {
// hash 表类型则查找 hash 表即可
sds value = hashTypeGetFromHashTable(o, field);
// 添加到输出缓冲
if (value == NULL)
// 响应为空
addReply(c, shared.nullbulk);
else
addReplyBulkCBuffer(c, value, sdslen(value));
} else {
serverPanic("Unknown hash encoding");
}
}
// t_hash.c, 从 ziplist 中查找 field 值
/* Get the value from a ziplist encoded hash, identified by field.
* Returns -1 when the field cannot be found. */
int hashTypeGetFromZiplist(robj *o, sds field,
unsigned char **vstr,
unsigned int *vlen,
long long *vll)
{
unsigned char *zl, *fptr = NULL, *vptr = NULL;
int ret; serverAssert(o->encoding == OBJ_ENCODING_ZIPLIST); zl = o->ptr;
fptr = ziplistIndex(zl, ZIPLIST_HEAD);
if (fptr != NULL) {
fptr = ziplistFind(fptr, (unsigned char*)field, sdslen(field), );
if (fptr != NULL) {
/* Grab pointer to the value (fptr points to the field) */
vptr = ziplistNext(zl, fptr);
serverAssert(vptr != NULL);
}
} if (vptr != NULL) {
ret = ziplistGet(vptr, vstr, vlen, vll);
serverAssert(ret);
return ;
} return -;
} // t_hash.c, 从hash表中查找 field 字段的值
/* Get the value from a hash table encoded hash, identified by field.
* Returns NULL when the field cannot be found, otherwise the SDS value
* is returned. */
sds hashTypeGetFromHashTable(robj *o, sds field) {
dictEntry *de; serverAssert(o->encoding == OBJ_ENCODING_HT); de = dictFind(o->ptr, field);
if (de == NULL) return NULL;
return dictGetVal(de);
}
四、hmget 批量获取值
与hget如出一辙。
// t_hash.c
void hmgetCommand(client *c) {
robj *o;
int i; /* Don't abort when the key cannot be found. Non-existing keys are empty
* hashes, where HMGET should respond with a series of null bulks. */
o = lookupKeyRead(c->db, c->argv[]);
if (o != NULL && o->type != OBJ_HASH) {
addReply(c, shared.wrongtypeerr);
return;
}
// 循环输出值
addReplyMultiBulkLen(c, c->argc-);
for (i = ; i < c->argc; i++) {
addHashFieldToReply(c, o, c->argv[i]->ptr);
}
}
五、hgetall 获取所有hash的kv
hgetall 和 hmget 方式稍微有点不一样，原因是为了让 hkeysCommand/hvalsCommand 进行复用。
// t_hash.c
void hgetallCommand(client *c) {
genericHgetallCommand(c,OBJ_HASH_KEY|OBJ_HASH_VALUE);
}
void genericHgetallCommand(client *c, int flags) {
robj *o;
hashTypeIterator *hi;
int multiplier = ;
int length, count = ; if ((o = lookupKeyReadOrReply(c,c->argv[],shared.emptymultibulk)) == NULL
|| checkType(c,o,OBJ_HASH)) return; if (flags & OBJ_HASH_KEY) multiplier++;
if (flags & OBJ_HASH_VALUE) multiplier++; length = hashTypeLength(o) * multiplier;
addReplyMultiBulkLen(c, length); hi = hashTypeInitIterator(o);
while (hashTypeNext(hi) != C_ERR) {
if (flags & OBJ_HASH_KEY) {
addHashIteratorCursorToReply(c, hi, OBJ_HASH_KEY);
count++;
}
if (flags & OBJ_HASH_VALUE) {
addHashIteratorCursorToReply(c, hi, OBJ_HASH_VALUE);
count++;
}
} hashTypeReleaseIterator(hi);
serverAssert(count == length);
}
static void addHashIteratorCursorToReply(client *c, hashTypeIterator *hi, int what) {
if (hi->encoding == OBJ_ENCODING_ZIPLIST) {
unsigned char *vstr = NULL;
unsigned int vlen = UINT_MAX;
long long vll = LLONG_MAX; hashTypeCurrentFromZiplist(hi, what, &vstr, &vlen, &vll);
if (vstr)
addReplyBulkCBuffer(c, vstr, vlen);
else
addReplyBulkLongLong(c, vll);
} else if (hi->encoding == OBJ_ENCODING_HT) {
sds value = hashTypeCurrentFromHashTable(hi, what);
addReplyBulkCBuffer(c, value, sdslen(value));
} else {
serverPanic("Unknown hash encoding");
}
}
六、hincrby 增加x某字段
hincrby key field 1
// t_hash.c,
void hincrbyCommand(client *c) {
long long value, incr, oldvalue;
robj *o;
sds new;
unsigned char *vstr;
unsigned int vlen;
// 解析增加字段值到 incr 中
if (getLongLongFromObjectOrReply(c,c->argv[],&incr,NULL) != C_OK) return;
// 获取原值或者设置为0
if ((o = hashTypeLookupWriteOrCreate(c,c->argv[])) == NULL) return;
if (hashTypeGetValue(o,c->argv[]->ptr,&vstr,&vlen,&value) == C_OK) {
if (vstr) {
if (string2ll((char*)vstr,vlen,&value) == ) {
addReplyError(c,"hash value is not an integer");
return;
}
} /* Else hashTypeGetValue() already stored it into &value */
} else {
value = ;
} oldvalue = value;
if ((incr < && oldvalue < && incr < (LLONG_MIN-oldvalue)) ||
(incr > && oldvalue > && incr > (LLONG_MAX-oldvalue))) {
addReplyError(c,"increment or decrement would overflow");
return;
}
// 将相加后的值重置设置回hash表中
value += incr;
new = sdsfromlonglong(value);
hashTypeSet(o,c->argv[]->ptr,new,HASH_SET_TAKE_VALUE);
addReplyLongLong(c,value);
signalModifiedKey(c->db,c->argv[]);
notifyKeyspaceEvent(NOTIFY_HASH,"hincrby",c->argv[],c->db->id);
server.dirty++;
}
七、hdel 删除某字段
hdel key field
// t_hash.c,
void hdelCommand(client *c) {
robj *o;
int j, deleted = , keyremoved = ; if ((o = lookupKeyWriteOrReply(c,c->argv[],shared.czero)) == NULL ||
checkType(c,o,OBJ_HASH)) return;
// 循环删除给定字段列表
for (j = ; j < c->argc; j++) {
if (hashTypeDelete(o,c->argv[j]->ptr)) {
deleted++;
// 当没有任何元素后，直接将key删除
if (hashTypeLength(o) == ) {
dbDelete(c->db,c->argv[]);
keyremoved = ;
break;
}
}
}
if (deleted) {
signalModifiedKey(c->db,c->argv[]);
notifyKeyspaceEvent(NOTIFY_HASH,"hdel",c->argv[],c->db->id);
if (keyremoved)
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",c->argv[],
c->db->id);
server.dirty += deleted;
}
addReplyLongLong(c,deleted);
}
// 具体删除 field, 同样区分编码类型，不同处理逻辑
/* Delete an element from a hash.
* Return 1 on deleted and 0 on not found. */
int hashTypeDelete(robj *o, sds field) {
int deleted = ; if (o->encoding == OBJ_ENCODING_ZIPLIST) {
unsigned char *zl, *fptr; zl = o->ptr;
fptr = ziplistIndex(zl, ZIPLIST_HEAD);
if (fptr != NULL) {
// ziplist 删除，依次删除 field, value
fptr = ziplistFind(fptr, (unsigned char*)field, sdslen(field), );
if (fptr != NULL) {
// ziplistDelete 为原地删除，所以只要调用2次，即把kv删除
zl = ziplistDelete(zl,&fptr);
zl = ziplistDelete(zl,&fptr);
o->ptr = zl;
deleted = ;
}
}
} else if (o->encoding == OBJ_ENCODING_HT) {
if (dictDelete((dict*)o->ptr, field) == C_OK) {
deleted = ; /* Always check if the dictionary needs a resize after a delete. */
// hash 删除的，可能需要进行缩容操作，这种处理方法相对特殊些
if (htNeedsResize(o->ptr)) dictResize(o->ptr);
} } else {
serverPanic("Unknown hash encoding");
}
return deleted;
}
// server.c, 是否需要进行 resize
int htNeedsResize(dict *dict) {
long long size, used; size = dictSlots(dict);
used = dictSize(dict);
// HASHTABLE_MIN_FILL=10, 即使用率小于 1/10 时，可以进行缩容操作了
return (size && used && size > DICT_HT_INITIAL_SIZE &&
(used*/size < HASHTABLE_MIN_FILL));
}
至此，整个hash数据结构的解析算是完整了。总体来说，hash由两种数据结构承载，ziplist在小数据量时使用，稍微复杂，但对于昂贵的内存来说是值得的。hash表在数据量大时使用，容易理解。通过本文的讲解，相信可以验证了你对redis hash 的实现的猜想了。