redis学习之RDB、AOF与复制时对过期键的处理教程

/* Iterate this DB writing every entry 
   *
   * 遍历数据库，并写入每个键值对的数据
   */
  while((de = dictNext(di)) != NULL) {
   sds keystr = dictGetKey(de);
   robj key, *o = dictGetVal(de);
   long long expire;
   
   // 根据 keystr ，在栈中创建一个 key 对象
   initStaticStringObject(key,keystr);

   // 获取键的过期时间
   expire = getExpire(db,&key);

   // 保存键值对数据
   if (rdbSaveKeyValuePair(&rdb,&key,o,expire,now) == -1) goto werr;
  }

/* Save a key-value pair, with expire time, type, key, value.
 *
 * 将键值对的键、值、过期时间和类型写入到 RDB 中。
 *
 * On error -1 is returned.
 *
 * 出错返回 -1 。
 *
 * On success if the key was actually saved 1 is returned, otherwise 0
 * is returned (the key was already expired). 
 *
 * 成功保存返回 1 ，当键已经过期时，返回 0 。
 */
int rdbSaveKeyValuePair(rio *rdb, robj *key, robj *val,
      long long expiretime, long long now)
{
 /* Save the expire time 
  *
  * 保存键的过期时间
  */
 if (expiretime != -1) {
  /* If this key is already expired skip it 
   *
   * 不写入已经过期的键
   */
  if (expiretime < now) return 0;

  if (rdbSaveType(rdb,REDIS_RDB_OPCODE_EXPIRETIME_MS) == -1) return -1;
  if (rdbSaveMillisecondTime(rdb,expiretime) == -1) return -1;
 }
 /* Save type, key, value 
  *
  * 保存类型，键，值
  */
 if (rdbSaveObjectType(rdb,val) == -1) return -1;
 if (rdbSaveStringObject(rdb,key) == -1) return -1;
 if (rdbSaveObject(rdb,val) == -1) return -1;
 return 1;
}

/* Check if the key already expired. This function is used when loading
   * an RDB file from disk, either at startup, or when an RDB was
   * received from the master. In the latter case, the master is
   * responsible for key expiry. If we would expire keys here, the
   * snapshot taken by the master may not be reflected on the slave. 
   *
   * 如果服务器为主节点的话，
   * 那么在键已经过期的时候，不再将它们关联到数据库中去
   */
  if (server.masterhost == NULL && expiretime != -1 && expiretime < now) {
   decrRefCount(key);
   decrRefCount(val);
   // 跳过
   continue;
  }