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RE: io thread very slow copying binlogs




Hi Brad,

> MySQL community edition 5.6.29, running Linux.
> 
> Binlogs never seem to get caught up on slaves.
> 
> I've done all I can, to validate that this isn't network or disk related.
> 
> Disk tests (using iostat and other methods) show lots of bandwidth left on
> the slave and master.
> 
> Network tests, such as:
> 
> - using scp to copy binlogs directly
> - using different NICs to copy binlogs
> - using mysqlbinlog to snag logs (the most 'real' way I can think to
>   simulate the replication thread copying binlogs from the master)
> 
> All seem to show that network speed is blazingly fast.
> 
> Yet, MySQL is barely getting 4mbit/sec across the network, and onto the
disk.
> And that's on a good day.
> 
> Any immediate suggestions here?  This seems very weird, and SQL thread is
> constantly running out of stuff to process.

Networking is not my strong-suit, but I have a suggestion:

Try lowering slave-net-timeout
http://dev.mysql.com/doc/refman/5.6/en/replication-options-slave.html#option
_mysqld_slave-net-timeout

I remember that we lowered the default in MySQL 5.7 (from 1hr to 60 seconds)
so that the connection between master/slave would be considered broken
faster.  If you have the throughput on a graph it might better explain if it
is a constant 4mbit/sec or more broken.


- Morgan


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