简单记录如下：

双主情况下跳过相同server id Event的方式：

- IO线程 通过对比SERVER_ID 进行跳过操作

```
    {
      mi->set_master_log_pos(mi->get_master_log_pos() + inc_pos);
      memcpy(rli->ign_master_log_name_end, mi->get_master_log_name(), FN_REFLEN); 
      DBUG_ASSERT(rli->ign_master_log_name_end[0]);
      rli->ign_master_log_pos_end= mi->get_master_log_pos();
    }
 ```

- SQL线程构造一个Rotate_log_event

```
        if (rli->ign_master_log_name_end[0])
        {
          /* We generate and return a Rotate, to make our positions advance */
          DBUG_PRINT("info",("seeing an ignored end segment"));
          ev= new Rotate_log_event(rli->ign_master_log_name_end,
                                   0, rli->ign_master_log_pos_end, exec_relay_log_event 
                                   Rotate_log_event::DUP_NAME);
          rli->ign_master_log_name_end[0]= 0;
          mysql_mutex_unlock(log_lock);exec_relay_log_event 
          if (unlikely(!ev))
          {
            errmsg= "Slave SQL thread failed to create a Rotate event "
              "(out of memory?), SHOW SLAVE STATUS may be inaccurate";
            goto err;
          }
          ev->server_id= 0; // don't be ignored by slave SQL thread
          DBUG_RETURN(ev);
        }
  ```

这样这些Event不会写入到relay log，SQL线程也不会读取，同时pos 也会做相应的增加。

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随笔：MySQL：双主情况下跳过Event的方式

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