redis之哈希命令源码解析

void hsetCommand(redisClient *c) {
    int update;
    robj *o;

    // 取出或新创建哈希对象
    if ((o = hashTypeLookupWriteOrCreate(c,c->argv[1])) == NULL) return;

    // 如果需要的话，转换哈希对象的编码
    hashTypeTryConversion(o,c->argv,2,3);

    // 编码 field 和 value 对象以节约空间
    hashTypeTryObjectEncoding(o,&c->argv[2], &c->argv[3]);

    // 设置 field 和 value 到 hash
    update = hashTypeSet(o,c->argv[2],c->argv[3]);

    // 返回状态：显示 field-value 对是新添加还是更新
    addReply(c, update ? shared.czero : shared.cone);

    // 发送键修改信号
    signalModifiedKey(c->db,c->argv[1]);

    // 发送事件通知
    notifyKeyspaceEvent(REDIS_NOTIFY_HASH,"hset",c->argv[1],c->db->id);

    // 将服务器设为脏
    server.dirty++;
}

void hashTypeTryConversion(robj *o, robj **argv, int start, int end) {
    int i;

    // 如果对象不是 ziplist 编码，那么直接返回
    if (o->encoding != REDIS_ENCODING_ZIPLIST) return;

    // 检查所有输入对象，看它们的字符串值是否超过了指定长度
    for (i = start; i <= end; i++) {
        if (sdsEncodedObject(argv[i]) &&
            sdslen(argv[i]->ptr) > server.hash_max_ziplist_value)
        {
            // 将对象的编码转换成 REDIS_ENCODING_HT
            hashTypeConvert(o, REDIS_ENCODING_HT);
            break;
        }
    }
}

if (hashTypeLength(o) > server.hash_max_ziplist_entries)
            hashTypeConvert(o, REDIS_ENCODING_HT);

int hashTypeDelete(robj *o, robj *field) {
    int deleted = 0;

    // 从 ziplist 中删除
    if (o->encoding == REDIS_ENCODING_ZIPLIST) {
        unsigned char *zl, *fptr;

        field = getDecodedObject(field);

        zl = o->ptr;
        fptr = ziplistIndex(zl, ZIPLIST_HEAD);
        if (fptr != NULL) {
            // 定位到域
            fptr = ziplistFind(fptr, field->ptr, sdslen(field->ptr), 1);
            if (fptr != NULL) {
                // 删除域和值
                zl = ziplistDelete(zl,&fptr);
                zl = ziplistDelete(zl,&fptr);
                o->ptr = zl;
                deleted = 1;
            }
        }

        decrRefCount(field);

    // 从字典中删除
    } else if (o->encoding == REDIS_ENCODING_HT) {
        if (dictDelete((dict*)o->ptr, field) == REDIS_OK) {
            deleted = 1;

            /* Always check if the dictionary needs a resize after a delete. */
            // 删除成功时，看字典是否需要收缩
            if (htNeedsResize(o->ptr)) dictResize(o->ptr);
        }

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

    return deleted;
}