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Re: MySQL Zombie Dump threads.
Posted by: Venkatesh Duggirala
Date: July 29, 2016 11:35AM

Hello Nicholas,

Could you please let us know

1) what is the value of the slave_net_timeout value ?
2) What is MySQL version that you are using ?
3) Are there any networks issues seen while this issue is happening?

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.

My guess is that you might be having some network issues and/or slave_net_timeout is set in your configuration is very less for your network settings and Slave might be thinking that it lost the connection with Master and thinks that it needs to establish the connection again.

Debugging in the direction of increasing the slave_net_timeout should eliminate this issue. Please note that starting from 5.7.7, we have
changed the default value to '60' seconds (it was 3600 before that)

More information about slave_net_timeout can be found here:
===========================================================
http://dev.mysql.com/doc/refman/5.7/en/replication-options-slave.html#option_mysqld_slave-net-timeout

Quote from the above link:
"Slave_net_timeout:
The number of seconds to wait for more data from the master before the slave considers the connection broken, aborts the read, and tries to reconnect. The first retry occurs immediately after the timeout."

Please do let me know if you have any more questions on this issue.

Regards,
Venkatesh

Senior Principal Member Technical Staff
MySQL Replication Developer
Oracle-Bangalore



Edited 1 time(s). Last edit at 07/29/2016 01:52PM by Edwin Desouza.

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