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I have setup a master and slave MySQL running 5.7.17 in Linux machines. Both servers have a unique UUID as specified in the auto.cnf file. Besides, the master server has server-id=10 while slave has server-id=20.

However I keep getting the following error coming in the master's error log. I could not figure out why as the replication is running fine. The error starts to come out when the master's SQL thread is stopped.

2016-12-28T09:00:37.953467Z 27931 [Note]
 Start binlog_dump to master_thread_id(27931) slave_server(20),
 pos(hostnameA-bin.000117, 818913948)
2016-12-28T09:01:38.027487Z 27978 [Note]
 While initializing dump thread for slave with UUID <xxxxxxxx-xxx-xxxx-8bbc-xxxxxxxxxxxx>,
 found a zombie dump thread with the same UUID.
 Master is killing the zombie dump thread(27931).
2016-12-28T09:01:38.027652Z 27978 [Note]
 Start binlog_dump to master_thread_id(27978) slave_server(20),
 pos(hostnameA-bin.000117, 818913948)
2016-12-28T09:02:38.104298Z 28025 [Note]
 While initializing dump thread for slave with UUID <xxxxxxxx-xxx-xxxx-8bbc-xxxxxxxxxxxx>,
 found a zombie dump thread with the same UUID.
 Master is killing the zombie dump thread(27978).
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Try to raise the slave_net_timeout. Prior to version 5.7.7, it was set to 3600, now to 60. Therefore, if you have any trouble on the network, the slave will think it has lost connection the server but when a Slave tries to [re]connect, it creates a dump thread on Master. Before Master creates a dump thread, it checks if there is already a dump thread running for that Slave (using the UUID value). If yes, it considers that old dump thread as "Zombie" dump thread and kills it. Creates a new one and prints this "Note" in the error log file. (This is cited from the official MySQL site )

Practically speaking: Enter MySQL on the slave machine and

mysql> set global slave_net_timeout=3600;

Restart your MySQL server and it should solve the problem.

Once this is OK, you can add this parameter in the configuration file my.conf to make the changes definitive.

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