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MySQL replication generate huge disk write IO
Posted by: Serge Shakhov
Date: May 30, 2013 05:30PM

Noticed that MySQL replication is generating enormous disk write activity

iotop 10-20Mb/s

AWS volume monitor - 700-800 IOPS

And it lasts for hours. Historical graphs show that this repeats every day for 8-10 hours.

Replication processes in the state: "Reading event from the relay log" and "Waiting for master to send event" Replication is lagging behind master, it is running but VERY slow.

There are no active processes in MySQL that can generate this activity. No backups at this time. Replication activity is constant but not so high to generate this problem.

If I stop slave SQL thread - activity drops to zero immediately. After starting slave it increases again. Stopping mysqld doesn't help.

What parameters/configs/metrics sould I check?

Any help would be appreciated.

Percona server 5.5 on CentOS
Replicated database about 500Gb, about 300 tables.

I have similar environment with 800Gb replicated DB with the same user activity but disk IO is 20 times lower.

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