Redis系列（十）：数据结构Hash之HDEL、HEXISTS、HGETALL、HKEYS、HLEN、HVALS命令

1.HDEL

从 key 指定的哈希集中移除指定的域。在哈希集中不存在的域将被忽略。

如果 key 指定的哈希集不存在，它将被认为是一个空的哈希集，该命令将返回0。

时间复杂度：O(N) N是被删除的字段数量

127.0.0.1:6379> hset myhash field1 "foo"
(integer) 1
127.0.0.1:6379> hdel myhash field1
(integer) 1
127.0.0.1:6379>

源码解析

// t_hash.c, 
void hdelCommand(client *c) {
    robj *o;
    int j, deleted = 0, keyremoved = 0;

    if ((o = lookupKeyWriteOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,o,OBJ_HASH)) return;
    // 循环删除给定字段列表
    for (j = 2; 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) == 0) {
                dbDelete(c->db,c->argv[1]);
                keyremoved = 1;
                break;
            }
        }
    }
    if (deleted) {
        signalModifiedKey(c->db,c->argv[1]);
        notifyKeyspaceEvent(NOTIFY_HASH,"hdel",c->argv[1],c->db->id);
        if (keyremoved)
            notifyKeyspaceEvent(NOTIFY_GENERIC,"del",c->argv[1],
                                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 = 0;

    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), 1);
            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 = 1;
            }
        }
    } else if (o->encoding == OBJ_ENCODING_HT) {
        if (dictDelete((dict*)o->ptr, field) == C_OK) {
            deleted = 1;

            /* 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*100/size < HASHTABLE_MIN_FILL));
}

2.HEXISTS

返回hash里面field是否存在

时间复杂度：O(1)

127.0.0.1:6379> hset myhash field1 "foo"
(integer) 1
127.0.0.1:6379> hexists myhash field1
(integer) 1
127.0.0.1:6379> hexists myhash field2
(integer) 0
127.0.0.1:6379>

源码解析

void hexistsCommand(client *c) {
    robj *o;
    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,o,OBJ_HASH)) return;

    addReply(c, hashTypeExists(o,c->argv[2]->ptr) ? shared.cone : shared.czero);
}

hashTypeExists

int hashTypeExists(robj *o, sds field) {
    if (o->encoding == OBJ_ENCODING_ZIPLIST) {
        unsigned char *vstr = NULL;
        unsigned int vlen = UINT_MAX;
        long long vll = LLONG_MAX;

        if (hashTypeGetFromZiplist(o, field, &vstr, &vlen, &vll) == 0) return 1;
    } else if (o->encoding == OBJ_ENCODING_HT) {
        if (hashTypeGetFromHashTable(o, field) != NULL) return 1;
    } else {
        serverPanic("Unknown hash encoding");
    }
    return 0;
}

ziplist的类型判断

/* 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), 1);
        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 0;
    }

    return -1;
}

ziplistFind

/* 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 = 0;
    unsigned char vencoding = 0;
    long long vll = 0;

    while (p[0] != ZIP_END) {
        unsigned int prevlensize, encoding, lensize, len;
        unsigned char *q;

        ZIP_DECODE_PREVLENSIZE(p, prevlensize);
        ZIP_DECODE_LENGTH(p + prevlensize, encoding, lensize, len);
        q = p + prevlensize + lensize;

        if (skipcnt == 0) {
            /* Compare current entry with specified entry */
            if (ZIP_IS_STR(encoding)) {
                if (len == vlen && memcmp(q, vstr, vlen) == 0) {
                    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 == 0) {
                    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 */
            skipcnt = skip;
        } else {
            /* Skip entry */
            skipcnt--;
        }

        /* Move to next entry */
        p = q + len;
    }

    return NULL;
}

hashtable类型的

/* 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);
}

dictFInd

dictEntry *dictFind(dict *d, const void *key)
{
    dictEntry *he;
    uint64_t h, idx, table;

    if (dictSize(d) == 0) return NULL; /* dict is empty */
    if (dictIsRehashing(d)) _dictRehashStep(d);
    h = dictHashKey(d, key);
    for (table = 0; table <= 1; table++) {
        idx = h & d->ht[table].sizemask;
        he = d->ht[table].table[idx];
        while(he) {
            if (key==he->key || dictCompareKeys(d, key, he->key))
                return he;
            he = he->next;
        }
        if (!dictIsRehashing(d)) return NULL;
    }
    return NULL;
}

3.HGETALL、HKEYS、HVALS

HGetAll：返回 key 指定的哈希集中所有的字段和值。返回值中，每个字段名的下一个是它的值，所以返回值的长度是哈希集大小的两倍

时间复杂度：O(N)

HKeys:返回 key 指定的哈希集中所有字段的名字。

时间复杂度：O(N)

HVals:返回 key 指定的哈希集中所有字段的值。

时间复杂度：O(N)

127.0.0.1:6379> hset myhash field1 "Hello"
(integer) 1
127.0.0.1:6379> hset myhash field2 "World"
(integer) 1
127.0.0.1:6379> hkeys myhash
1) "field1"
2) "field2"
127.0.0.1:6379> hgetall myhash
1) "field1"
2) "Hello"
3) "field2"
4) "World"
127.0.0.1:6379> hvals myhash
1) "Hello"
2) "World"
127.0.0.1:6379>

源码解析

void hkeysCommand(client *c) {
    genericHgetallCommand(c,OBJ_HASH_KEY);
}

void hvalsCommand(client *c) {
    genericHgetallCommand(c,OBJ_HASH_VALUE);
}

void hgetallCommand(client *c) {
    genericHgetallCommand(c,OBJ_HASH_KEY|OBJ_HASH_VALUE);
}

void genericHgetallCommand(client *c, int flags) {
    robj *o;
    hashTypeIterator *hi;
    int length, count = 0;

    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.emptymap[c->resp]))
        == NULL || checkType(c,o,OBJ_HASH)) return;

    /* We return a map if the user requested keys and values, like in the
     * HGETALL case. Otherwise to use a flat array makes more sense. */
    length = hashTypeLength(o);
    if (flags & OBJ_HASH_KEY && flags & OBJ_HASH_VALUE) {
        addReplyMapLen(c, length);
    } else {
        addReplyArrayLen(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);

    /* Make sure we returned the right number of elements. */
    if (flags & OBJ_HASH_KEY && flags & OBJ_HASH_VALUE) count /= 2;
    serverAssert(count == length);
}

4.HLEN

返回 key 指定的哈希集包含的字段的数量。

时间复杂度：O(1)

127.0.0.1:6379> hlen myhash
(integer) 2
127.0.0.1:6379>

void hlenCommand(client *c) {
    robj *o;

    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,o,OBJ_HASH)) return;

    addReplyLongLong(c,hashTypeLength(o));
}

/* Return the number of elements in a hash. */
unsigned long hashTypeLength(const robj *o) {
    unsigned long length = ULONG_MAX;

    if (o->encoding == OBJ_ENCODING_ZIPLIST) {
        length = ziplistLen(o->ptr) / 2;
    } else if (o->encoding == OBJ_ENCODING_HT) {
        length = dictSize((const dict*)o->ptr);
    } else {
        serverPanic("Unknown hash encoding");
    }
    return length;
}