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Re: io thread very slow copying binlogs





Hey Morgan,

Thanks for the tip.  Might come in handy.

But, I'm positive it's not a disconnect / reconnect thing.  Or, at least
not one affected by that timeout.

I can do a watch ls -lh in the binlog dir, and see the relay log
increasing in size by a M every 4 or 5 seconds or so.  About
200kbyte/sec / 1.6Mbit/sec right now.

It seems very steady too.  As in, if I look at bytes, they're constantly
increasing.. just, slow..

On Fri, 20 Jan 2017 10:19:57 -0500
"Morgan Tocker" <morgan.tocker@xxxxxxxxxx> wrote:

> 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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